/* * Read-Copy Update mechanism for mutual exclusion * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * * Authors: Dipankar Sarma * Manfred Spraul * Paul E. McKenney Hierarchical version * * Based on the original work by Paul McKenney * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * * For detailed explanation of Read-Copy Update mechanism see - * Documentation/RCU */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include "tree.h" #include "rcu.h" MODULE_ALIAS("rcutree"); #ifdef MODULE_PARAM_PREFIX #undef MODULE_PARAM_PREFIX #endif #define MODULE_PARAM_PREFIX "rcutree." /* Data structures. */ static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS]; /* * In order to export the rcu_state name to the tracing tools, it * needs to be added in the __tracepoint_string section. * This requires defining a separate variable tp__varname * that points to the string being used, and this will allow * the tracing userspace tools to be able to decipher the string * address to the matching string. */ #ifdef CONFIG_TRACING # define DEFINE_RCU_TPS(sname) \ static char sname##_varname[] = #sname; \ static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; # define RCU_STATE_NAME(sname) sname##_varname #else # define DEFINE_RCU_TPS(sname) # define RCU_STATE_NAME(sname) __stringify(sname) #endif #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \ DEFINE_RCU_TPS(sname) \ static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \ struct rcu_state sname##_state = { \ .level = { &sname##_state.node[0] }, \ .rda = &sname##_data, \ .call = cr, \ .fqs_state = RCU_GP_IDLE, \ .gpnum = 0UL - 300UL, \ .completed = 0UL - 300UL, \ .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \ .orphan_nxttail = &sname##_state.orphan_nxtlist, \ .orphan_donetail = &sname##_state.orphan_donelist, \ .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \ .name = RCU_STATE_NAME(sname), \ .abbr = sabbr, \ } RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched); RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh); static struct rcu_state *const rcu_state_p; static struct rcu_data __percpu *const rcu_data_p; LIST_HEAD(rcu_struct_flavors); /* Dump rcu_node combining tree at boot to verify correct setup. */ static bool dump_tree; module_param(dump_tree, bool, 0444); /* Control rcu_node-tree auto-balancing at boot time. */ static bool rcu_fanout_exact; module_param(rcu_fanout_exact, bool, 0444); /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */ static int rcu_fanout_leaf = RCU_FANOUT_LEAF; module_param(rcu_fanout_leaf, int, 0444); int rcu_num_lvls __read_mostly = RCU_NUM_LVLS; static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */ NUM_RCU_LVL_0, NUM_RCU_LVL_1, NUM_RCU_LVL_2, NUM_RCU_LVL_3, NUM_RCU_LVL_4, }; int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */ /* * The rcu_scheduler_active variable transitions from zero to one just * before the first task is spawned. So when this variable is zero, RCU * can assume that there is but one task, allowing RCU to (for example) * optimize synchronize_sched() to a simple barrier(). When this variable * is one, RCU must actually do all the hard work required to detect real * grace periods. This variable is also used to suppress boot-time false * positives from lockdep-RCU error checking. */ int rcu_scheduler_active __read_mostly; EXPORT_SYMBOL_GPL(rcu_scheduler_active); /* * The rcu_scheduler_fully_active variable transitions from zero to one * during the early_initcall() processing, which is after the scheduler * is capable of creating new tasks. So RCU processing (for example, * creating tasks for RCU priority boosting) must be delayed until after * rcu_scheduler_fully_active transitions from zero to one. We also * currently delay invocation of any RCU callbacks until after this point. * * It might later prove better for people registering RCU callbacks during * early boot to take responsibility for these callbacks, but one step at * a time. */ static int rcu_scheduler_fully_active __read_mostly; static void rcu_init_new_rnp(struct rcu_node *rnp_leaf); static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf); static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu); static void invoke_rcu_core(void); static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp); /* rcuc/rcub kthread realtime priority */ #ifdef CONFIG_RCU_KTHREAD_PRIO static int kthread_prio = CONFIG_RCU_KTHREAD_PRIO; #else /* #ifdef CONFIG_RCU_KTHREAD_PRIO */ static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; #endif /* #else #ifdef CONFIG_RCU_KTHREAD_PRIO */ module_param(kthread_prio, int, 0644); /* Delay in jiffies for grace-period initialization delays, debug only. */ #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT static int gp_preinit_delay = CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT_DELAY; module_param(gp_preinit_delay, int, 0644); #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */ static const int gp_preinit_delay; #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_PREINIT */ #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT static int gp_init_delay = CONFIG_RCU_TORTURE_TEST_SLOW_INIT_DELAY; module_param(gp_init_delay, int, 0644); #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ static const int gp_init_delay; #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_INIT */ #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP static int gp_cleanup_delay = CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP_DELAY; module_param(gp_cleanup_delay, int, 0644); #else /* #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */ static const int gp_cleanup_delay; #endif /* #else #ifdef CONFIG_RCU_TORTURE_TEST_SLOW_CLEANUP */ /* * Number of grace periods between delays, normalized by the duration of * the delay. The longer the the delay, the more the grace periods between * each delay. The reason for this normalization is that it means that, * for non-zero delays, the overall slowdown of grace periods is constant * regardless of the duration of the delay. This arrangement balances * the need for long delays to increase some race probabilities with the * need for fast grace periods to increase other race probabilities. */ #define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */ /* * Track the rcutorture test sequence number and the update version * number within a given test. The rcutorture_testseq is incremented * on every rcutorture module load and unload, so has an odd value * when a test is running. The rcutorture_vernum is set to zero * when rcutorture starts and is incremented on each rcutorture update. * These variables enable correlating rcutorture output with the * RCU tracing information. */ unsigned long rcutorture_testseq; unsigned long rcutorture_vernum; /* * Compute the mask of online CPUs for the specified rcu_node structure. * This will not be stable unless the rcu_node structure's ->lock is * held, but the bit corresponding to the current CPU will be stable * in most contexts. */ unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp) { return READ_ONCE(rnp->qsmaskinitnext); } /* * Return true if an RCU grace period is in progress. The READ_ONCE()s * permit this function to be invoked without holding the root rcu_node * structure's ->lock, but of course results can be subject to change. */ static int rcu_gp_in_progress(struct rcu_state *rsp) { return READ_ONCE(rsp->completed) != READ_ONCE(rsp->gpnum); } /* * Note a quiescent state. Because we do not need to know * how many quiescent states passed, just if there was at least * one since the start of the grace period, this just sets a flag. * The caller must have disabled preemption. */ void rcu_sched_qs(void) { if (!__this_cpu_read(rcu_sched_data.passed_quiesce)) { trace_rcu_grace_period(TPS("rcu_sched"), __this_cpu_read(rcu_sched_data.gpnum), TPS("cpuqs")); __this_cpu_write(rcu_sched_data.passed_quiesce, 1); } } void rcu_bh_qs(void) { if (!__this_cpu_read(rcu_bh_data.passed_quiesce)) { trace_rcu_grace_period(TPS("rcu_bh"), __this_cpu_read(rcu_bh_data.gpnum), TPS("cpuqs")); __this_cpu_write(rcu_bh_data.passed_quiesce, 1); } } static DEFINE_PER_CPU(int, rcu_sched_qs_mask); static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE, .dynticks = ATOMIC_INIT(1), #ifdef CONFIG_NO_HZ_FULL_SYSIDLE .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE, .dynticks_idle = ATOMIC_INIT(1), #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ }; DEFINE_PER_CPU_SHARED_ALIGNED(unsigned long, rcu_qs_ctr); EXPORT_PER_CPU_SYMBOL_GPL(rcu_qs_ctr); /* * Let the RCU core know that this CPU has gone through the scheduler, * which is a quiescent state. This is called when the need for a * quiescent state is urgent, so we burn an atomic operation and full * memory barriers to let the RCU core know about it, regardless of what * this CPU might (or might not) do in the near future. * * We inform the RCU core by emulating a zero-duration dyntick-idle * period, which we in turn do by incrementing the ->dynticks counter * by two. */ static void rcu_momentary_dyntick_idle(void) { unsigned long flags; struct rcu_data *rdp; struct rcu_dynticks *rdtp; int resched_mask; struct rcu_state *rsp; local_irq_save(flags); /* * Yes, we can lose flag-setting operations. This is OK, because * the flag will be set again after some delay. */ resched_mask = raw_cpu_read(rcu_sched_qs_mask); raw_cpu_write(rcu_sched_qs_mask, 0); /* Find the flavor that needs a quiescent state. */ for_each_rcu_flavor(rsp) { rdp = raw_cpu_ptr(rsp->rda); if (!(resched_mask & rsp->flavor_mask)) continue; smp_mb(); /* rcu_sched_qs_mask before cond_resched_completed. */ if (READ_ONCE(rdp->mynode->completed) != READ_ONCE(rdp->cond_resched_completed)) continue; /* * Pretend to be momentarily idle for the quiescent state. * This allows the grace-period kthread to record the * quiescent state, with no need for this CPU to do anything * further. */ rdtp = this_cpu_ptr(&rcu_dynticks); smp_mb__before_atomic(); /* Earlier stuff before QS. */ atomic_add(2, &rdtp->dynticks); /* QS. */ smp_mb__after_atomic(); /* Later stuff after QS. */ break; } local_irq_restore(flags); } /* * Note a context switch. This is a quiescent state for RCU-sched, * and requires special handling for preemptible RCU. * The caller must have disabled preemption. */ void rcu_note_context_switch(void) { trace_rcu_utilization(TPS("Start context switch")); rcu_sched_qs(); rcu_preempt_note_context_switch(); if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) rcu_momentary_dyntick_idle(); trace_rcu_utilization(TPS("End context switch")); } EXPORT_SYMBOL_GPL(rcu_note_context_switch); /* * Register a quiescent state for all RCU flavors. If there is an * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight * dyntick-idle quiescent state visible to other CPUs (but only for those * RCU flavors in desperate need of a quiescent state, which will normally * be none of them). Either way, do a lightweight quiescent state for * all RCU flavors. */ void rcu_all_qs(void) { if (unlikely(raw_cpu_read(rcu_sched_qs_mask))) rcu_momentary_dyntick_idle(); this_cpu_inc(rcu_qs_ctr); } EXPORT_SYMBOL_GPL(rcu_all_qs); static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */ static long qhimark = 10000; /* If this many pending, ignore blimit. */ static long qlowmark = 100; /* Once only this many pending, use blimit. */ module_param(blimit, long, 0444); module_param(qhimark, long, 0444); module_param(qlowmark, long, 0444); static ulong jiffies_till_first_fqs = ULONG_MAX; static ulong jiffies_till_next_fqs = ULONG_MAX; module_param(jiffies_till_first_fqs, ulong, 0644); module_param(jiffies_till_next_fqs, ulong, 0644); /* * How long the grace period must be before we start recruiting * quiescent-state help from rcu_note_context_switch(). */ static ulong jiffies_till_sched_qs = HZ / 20; module_param(jiffies_till_sched_qs, ulong, 0644); static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp); static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp, bool *isidle, unsigned long *maxj), bool *isidle, unsigned long *maxj); static void force_quiescent_state(struct rcu_state *rsp); static int rcu_pending(void); /* * Return the number of RCU batches started thus far for debug & stats. */ unsigned long rcu_batches_started(void) { return rcu_state_p->gpnum; } EXPORT_SYMBOL_GPL(rcu_batches_started); /* * Return the number of RCU-sched batches started thus far for debug & stats. */ unsigned long rcu_batches_started_sched(void) { return rcu_sched_state.gpnum; } EXPORT_SYMBOL_GPL(rcu_batches_started_sched); /* * Return the number of RCU BH batches started thus far for debug & stats. */ unsigned long rcu_batches_started_bh(void) { return rcu_bh_state.gpnum; } EXPORT_SYMBOL_GPL(rcu_batches_started_bh); /* * Return the number of RCU batches completed thus far for debug & stats. */ unsigned long rcu_batches_completed(void) { return rcu_state_p->completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Return the number of RCU-sched batches completed thus far for debug & stats. */ unsigned long rcu_batches_completed_sched(void) { return rcu_sched_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_sched); /* * Return the number of RCU BH batches completed thus far for debug & stats. */ unsigned long rcu_batches_completed_bh(void) { return rcu_bh_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); /* * Force a quiescent state. */ void rcu_force_quiescent_state(void) { force_quiescent_state(rcu_state_p); } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); /* * Force a quiescent state for RCU BH. */ void rcu_bh_force_quiescent_state(void) { force_quiescent_state(&rcu_bh_state); } EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state); /* * Force a quiescent state for RCU-sched. */ void rcu_sched_force_quiescent_state(void) { force_quiescent_state(&rcu_sched_state); } EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state); /* * Show the state of the grace-period kthreads. */ void show_rcu_gp_kthreads(void) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) { pr_info("%s: wait state: %d ->state: %#lx\n", rsp->name, rsp->gp_state, rsp->gp_kthread->state); /* sched_show_task(rsp->gp_kthread); */ } } EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads); /* * Record the number of times rcutorture tests have been initiated and * terminated. This information allows the debugfs tracing stats to be * correlated to the rcutorture messages, even when the rcutorture module * is being repeatedly loaded and unloaded. In other words, we cannot * store this state in rcutorture itself. */ void rcutorture_record_test_transition(void) { rcutorture_testseq++; rcutorture_vernum = 0; } EXPORT_SYMBOL_GPL(rcutorture_record_test_transition); /* * Send along grace-period-related data for rcutorture diagnostics. */ void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags, unsigned long *gpnum, unsigned long *completed) { struct rcu_state *rsp = NULL; switch (test_type) { case RCU_FLAVOR: rsp = rcu_state_p; break; case RCU_BH_FLAVOR: rsp = &rcu_bh_state; break; case RCU_SCHED_FLAVOR: rsp = &rcu_sched_state; break; default: break; } if (rsp != NULL) { *flags = READ_ONCE(rsp->gp_flags); *gpnum = READ_ONCE(rsp->gpnum); *completed = READ_ONCE(rsp->completed); return; } *flags = 0; *gpnum = 0; *completed = 0; } EXPORT_SYMBOL_GPL(rcutorture_get_gp_data); /* * Record the number of writer passes through the current rcutorture test. * This is also used to correlate debugfs tracing stats with the rcutorture * messages. */ void rcutorture_record_progress(unsigned long vernum) { rcutorture_vernum++; } EXPORT_SYMBOL_GPL(rcutorture_record_progress); /* * Does the CPU have callbacks ready to be invoked? */ static int cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp) { return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] && rdp->nxttail[RCU_DONE_TAIL] != NULL; } /* * Return the root node of the specified rcu_state structure. */ static struct rcu_node *rcu_get_root(struct rcu_state *rsp) { return &rsp->node[0]; } /* * Is there any need for future grace periods? * Interrupts must be disabled. If the caller does not hold the root * rnp_node structure's ->lock, the results are advisory only. */ static int rcu_future_needs_gp(struct rcu_state *rsp) { struct rcu_node *rnp = rcu_get_root(rsp); int idx = (READ_ONCE(rnp->completed) + 1) & 0x1; int *fp = &rnp->need_future_gp[idx]; return READ_ONCE(*fp); } /* * Does the current CPU require a not-yet-started grace period? * The caller must have disabled interrupts to prevent races with * normal callback registry. */ static int cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp) { int i; if (rcu_gp_in_progress(rsp)) return 0; /* No, a grace period is already in progress. */ if (rcu_future_needs_gp(rsp)) return 1; /* Yes, a no-CBs CPU needs one. */ if (!rdp->nxttail[RCU_NEXT_TAIL]) return 0; /* No, this is a no-CBs (or offline) CPU. */ if (*rdp->nxttail[RCU_NEXT_READY_TAIL]) return 1; /* Yes, this CPU has newly registered callbacks. */ for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) if (rdp->nxttail[i - 1] != rdp->nxttail[i] && ULONG_CMP_LT(READ_ONCE(rsp->completed), rdp->nxtcompleted[i])) return 1; /* Yes, CBs for future grace period. */ return 0; /* No grace period needed. */ } /* * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state * * If the new value of the ->dynticks_nesting counter now is zero, * we really have entered idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ static void rcu_eqs_enter_common(long long oldval, bool user) { struct rcu_state *rsp; struct rcu_data *rdp; struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting); if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)) { struct task_struct *idle __maybe_unused = idle_task(smp_processor_id()); trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0); ftrace_dump(DUMP_ORIG); WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } for_each_rcu_flavor(rsp) { rdp = this_cpu_ptr(rsp->rda); do_nocb_deferred_wakeup(rdp); } rcu_prepare_for_idle(); /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ smp_mb__before_atomic(); /* See above. */ atomic_inc(&rdtp->dynticks); smp_mb__after_atomic(); /* Force ordering with next sojourn. */ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && atomic_read(&rdtp->dynticks) & 0x1); rcu_dynticks_task_enter(); /* * It is illegal to enter an extended quiescent state while * in an RCU read-side critical section. */ rcu_lockdep_assert(!lock_is_held(&rcu_lock_map), "Illegal idle entry in RCU read-side critical section."); rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map), "Illegal idle entry in RCU-bh read-side critical section."); rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map), "Illegal idle entry in RCU-sched read-side critical section."); } /* * Enter an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. */ static void rcu_eqs_enter(bool user) { long long oldval; struct rcu_dynticks *rdtp; rdtp = this_cpu_ptr(&rcu_dynticks); oldval = rdtp->dynticks_nesting; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && (oldval & DYNTICK_TASK_NEST_MASK) == 0); if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) { rdtp->dynticks_nesting = 0; rcu_eqs_enter_common(oldval, user); } else { rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE; } } /** * rcu_idle_enter - inform RCU that current CPU is entering idle * * Enter idle mode, in other words, -leave- the mode in which RCU * read-side critical sections can occur. (Though RCU read-side * critical sections can occur in irq handlers in idle, a possibility * handled by irq_enter() and irq_exit().) * * We crowbar the ->dynticks_nesting field to zero to allow for * the possibility of usermode upcalls having messed up our count * of interrupt nesting level during the prior busy period. */ void rcu_idle_enter(void) { unsigned long flags; local_irq_save(flags); rcu_eqs_enter(false); rcu_sysidle_enter(0); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_enter); #ifdef CONFIG_NO_HZ_FULL /** * rcu_user_enter - inform RCU that we are resuming userspace. * * Enter RCU idle mode right before resuming userspace. No use of RCU * is permitted between this call and rcu_user_exit(). This way the * CPU doesn't need to maintain the tick for RCU maintenance purposes * when the CPU runs in userspace. */ void rcu_user_enter(void) { rcu_eqs_enter(1); } #endif /* CONFIG_NO_HZ_FULL */ /** * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle * * Exit from an interrupt handler, which might possibly result in entering * idle mode, in other words, leaving the mode in which read-side critical * sections can occur. * * This code assumes that the idle loop never does anything that might * result in unbalanced calls to irq_enter() and irq_exit(). If your * architecture violates this assumption, RCU will give you what you * deserve, good and hard. But very infrequently and irreproducibly. * * Use things like work queues to work around this limitation. * * You have been warned. */ void rcu_irq_exit(void) { unsigned long flags; long long oldval; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = this_cpu_ptr(&rcu_dynticks); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting--; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && rdtp->dynticks_nesting < 0); if (rdtp->dynticks_nesting) trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting); else rcu_eqs_enter_common(oldval, true); rcu_sysidle_enter(1); local_irq_restore(flags); } /* * rcu_eqs_exit_common - current CPU moving away from extended quiescent state * * If the new value of the ->dynticks_nesting counter was previously zero, * we really have exited idle, and must do the appropriate accounting. * The caller must have disabled interrupts. */ static void rcu_eqs_exit_common(long long oldval, int user) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); rcu_dynticks_task_exit(); smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */ atomic_inc(&rdtp->dynticks); /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ smp_mb__after_atomic(); /* See above. */ WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !(atomic_read(&rdtp->dynticks) & 0x1)); rcu_cleanup_after_idle(); trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting); if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current)) { struct task_struct *idle __maybe_unused = idle_task(smp_processor_id()); trace_rcu_dyntick(TPS("Error on exit: not idle task"), oldval, rdtp->dynticks_nesting); ftrace_dump(DUMP_ORIG); WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s", current->pid, current->comm, idle->pid, idle->comm); /* must be idle task! */ } } /* * Exit an RCU extended quiescent state, which can be either the * idle loop or adaptive-tickless usermode execution. */ static void rcu_eqs_exit(bool user) { struct rcu_dynticks *rdtp; long long oldval; rdtp = this_cpu_ptr(&rcu_dynticks); oldval = rdtp->dynticks_nesting; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0); if (oldval & DYNTICK_TASK_NEST_MASK) { rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE; } else { rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_eqs_exit_common(oldval, user); } } /** * rcu_idle_exit - inform RCU that current CPU is leaving idle * * Exit idle mode, in other words, -enter- the mode in which RCU * read-side critical sections can occur. * * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to * allow for the possibility of usermode upcalls messing up our count * of interrupt nesting level during the busy period that is just * now starting. */ void rcu_idle_exit(void) { unsigned long flags; local_irq_save(flags); rcu_eqs_exit(false); rcu_sysidle_exit(0); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(rcu_idle_exit); #ifdef CONFIG_NO_HZ_FULL /** * rcu_user_exit - inform RCU that we are exiting userspace. * * Exit RCU idle mode while entering the kernel because it can * run a RCU read side critical section anytime. */ void rcu_user_exit(void) { rcu_eqs_exit(1); } #endif /* CONFIG_NO_HZ_FULL */ /** * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle * * Enter an interrupt handler, which might possibly result in exiting * idle mode, in other words, entering the mode in which read-side critical * sections can occur. * * Note that the Linux kernel is fully capable of entering an interrupt * handler that it never exits, for example when doing upcalls to * user mode! This code assumes that the idle loop never does upcalls to * user mode. If your architecture does do upcalls from the idle loop (or * does anything else that results in unbalanced calls to the irq_enter() * and irq_exit() functions), RCU will give you what you deserve, good * and hard. But very infrequently and irreproducibly. * * Use things like work queues to work around this limitation. * * You have been warned. */ void rcu_irq_enter(void) { unsigned long flags; struct rcu_dynticks *rdtp; long long oldval; local_irq_save(flags); rdtp = this_cpu_ptr(&rcu_dynticks); oldval = rdtp->dynticks_nesting; rdtp->dynticks_nesting++; WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && rdtp->dynticks_nesting == 0); if (oldval) trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting); else rcu_eqs_exit_common(oldval, true); rcu_sysidle_exit(1); local_irq_restore(flags); } /** * rcu_nmi_enter - inform RCU of entry to NMI context * * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know * that the CPU is active. This implementation permits nested NMIs, as * long as the nesting level does not overflow an int. (You will probably * run out of stack space first.) */ void rcu_nmi_enter(void) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); int incby = 2; /* Complain about underflow. */ WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0); /* * If idle from RCU viewpoint, atomically increment ->dynticks * to mark non-idle and increment ->dynticks_nmi_nesting by one. * Otherwise, increment ->dynticks_nmi_nesting by two. This means * if ->dynticks_nmi_nesting is equal to one, we are guaranteed * to be in the outermost NMI handler that interrupted an RCU-idle * period (observation due to Andy Lutomirski). */ if (!(atomic_read(&rdtp->dynticks) & 0x1)) { smp_mb__before_atomic(); /* Force delay from prior write. */ atomic_inc(&rdtp->dynticks); /* atomic_inc() before later RCU read-side crit sects */ smp_mb__after_atomic(); /* See above. */ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); incby = 1; } rdtp->dynticks_nmi_nesting += incby; barrier(); } /** * rcu_nmi_exit - inform RCU of exit from NMI context * * If we are returning from the outermost NMI handler that interrupted an * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting * to let the RCU grace-period handling know that the CPU is back to * being RCU-idle. */ void rcu_nmi_exit(void) { struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); /* * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks. * (We are exiting an NMI handler, so RCU better be paying attention * to us!) */ WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0); WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); /* * If the nesting level is not 1, the CPU wasn't RCU-idle, so * leave it in non-RCU-idle state. */ if (rdtp->dynticks_nmi_nesting != 1) { rdtp->dynticks_nmi_nesting -= 2; return; } /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ rdtp->dynticks_nmi_nesting = 0; /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ smp_mb__before_atomic(); /* See above. */ atomic_inc(&rdtp->dynticks); smp_mb__after_atomic(); /* Force delay to next write. */ WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); } /** * __rcu_is_watching - are RCU read-side critical sections safe? * * Return true if RCU is watching the running CPU, which means that * this CPU can safely enter RCU read-side critical sections. Unlike * rcu_is_watching(), the caller of __rcu_is_watching() must have at * least disabled preemption. */ bool notrace __rcu_is_watching(void) { return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1; } /** * rcu_is_watching - see if RCU thinks that the current CPU is idle * * If the current CPU is in its idle loop and is neither in an interrupt * or NMI handler, return true. */ bool notrace rcu_is_watching(void) { bool ret; preempt_disable(); ret = __rcu_is_watching(); preempt_enable(); return ret; } EXPORT_SYMBOL_GPL(rcu_is_watching); #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) /* * Is the current CPU online? Disable preemption to avoid false positives * that could otherwise happen due to the current CPU number being sampled, * this task being preempted, its old CPU being taken offline, resuming * on some other CPU, then determining that its old CPU is now offline. * It is OK to use RCU on an offline processor during initial boot, hence * the check for rcu_scheduler_fully_active. Note also that it is OK * for a CPU coming online to use RCU for one jiffy prior to marking itself * online in the cpu_online_mask. Similarly, it is OK for a CPU going * offline to continue to use RCU for one jiffy after marking itself * offline in the cpu_online_mask. This leniency is necessary given the * non-atomic nature of the online and offline processing, for example, * the fact that a CPU enters the scheduler after completing the CPU_DYING * notifiers. * * This is also why RCU internally marks CPUs online during the * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase. * * Disable checking if in an NMI handler because we cannot safely report * errors from NMI handlers anyway. */ bool rcu_lockdep_current_cpu_online(void) { struct rcu_data *rdp; struct rcu_node *rnp; bool ret; if (in_nmi()) return true; preempt_disable(); rdp = this_cpu_ptr(&rcu_sched_data); rnp = rdp->mynode; ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) || !rcu_scheduler_fully_active; preempt_enable(); return ret; } EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online); #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */ /** * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle * * If the current CPU is idle or running at a first-level (not nested) * interrupt from idle, return true. The caller must have at least * disabled preemption. */ static int rcu_is_cpu_rrupt_from_idle(void) { return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1; } /* * Snapshot the specified CPU's dynticks counter so that we can later * credit them with an implicit quiescent state. Return 1 if this CPU * is in dynticks idle mode, which is an extended quiescent state. */ static int dyntick_save_progress_counter(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks); rcu_sysidle_check_cpu(rdp, isidle, maxj); if ((rdp->dynticks_snap & 0x1) == 0) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); return 1; } else { if (ULONG_CMP_LT(READ_ONCE(rdp->gpnum) + ULONG_MAX / 4, rdp->mynode->gpnum)) WRITE_ONCE(rdp->gpwrap, true); return 0; } } /* * Return true if the specified CPU has passed through a quiescent * state by virtue of being in or having passed through an dynticks * idle state since the last call to dyntick_save_progress_counter() * for this same CPU, or by virtue of having been offline. */ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { unsigned int curr; int *rcrmp; unsigned int snap; curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks); snap = (unsigned int)rdp->dynticks_snap; /* * If the CPU passed through or entered a dynticks idle phase with * no active irq/NMI handlers, then we can safely pretend that the CPU * already acknowledged the request to pass through a quiescent * state. Either way, that CPU cannot possibly be in an RCU * read-side critical section that started before the beginning * of the current RCU grace period. */ if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); rdp->dynticks_fqs++; return 1; } /* * Check for the CPU being offline, but only if the grace period * is old enough. We don't need to worry about the CPU changing * state: If we see it offline even once, it has been through a * quiescent state. * * The reason for insisting that the grace period be at least * one jiffy old is that CPUs that are not quite online and that * have just gone offline can still execute RCU read-side critical * sections. */ if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies)) return 0; /* Grace period is not old enough. */ barrier(); if (cpu_is_offline(rdp->cpu)) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl")); rdp->offline_fqs++; return 1; } /* * A CPU running for an extended time within the kernel can * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode, * even context-switching back and forth between a pair of * in-kernel CPU-bound tasks cannot advance grace periods. * So if the grace period is old enough, make the CPU pay attention. * Note that the unsynchronized assignments to the per-CPU * rcu_sched_qs_mask variable are safe. Yes, setting of * bits can be lost, but they will be set again on the next * force-quiescent-state pass. So lost bit sets do not result * in incorrect behavior, merely in a grace period lasting * a few jiffies longer than it might otherwise. Because * there are at most four threads involved, and because the * updates are only once every few jiffies, the probability of * lossage (and thus of slight grace-period extension) is * quite low. * * Note that if the jiffies_till_sched_qs boot/sysfs parameter * is set too high, we override with half of the RCU CPU stall * warning delay. */ rcrmp = &per_cpu(rcu_sched_qs_mask, rdp->cpu); if (ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs) || ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) { if (!(READ_ONCE(*rcrmp) & rdp->rsp->flavor_mask)) { WRITE_ONCE(rdp->cond_resched_completed, READ_ONCE(rdp->mynode->completed)); smp_mb(); /* ->cond_resched_completed before *rcrmp. */ WRITE_ONCE(*rcrmp, READ_ONCE(*rcrmp) + rdp->rsp->flavor_mask); resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ rdp->rsp->jiffies_resched += 5; /* Enable beating. */ } else if (ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) { /* Time to beat on that CPU again! */ resched_cpu(rdp->cpu); /* Force CPU into scheduler. */ rdp->rsp->jiffies_resched += 5; /* Re-enable beating. */ } } return 0; } static void record_gp_stall_check_time(struct rcu_state *rsp) { unsigned long j = jiffies; unsigned long j1; rsp->gp_start = j; smp_wmb(); /* Record start time before stall time. */ j1 = rcu_jiffies_till_stall_check(); WRITE_ONCE(rsp->jiffies_stall, j + j1); rsp->jiffies_resched = j + j1 / 2; rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs); } /* * Complain about starvation of grace-period kthread. */ static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp) { unsigned long gpa; unsigned long j; j = jiffies; gpa = READ_ONCE(rsp->gp_activity); if (j - gpa > 2 * HZ) pr_err("%s kthread starved for %ld jiffies! g%lu c%lu f%#x\n", rsp->name, j - gpa, rsp->gpnum, rsp->completed, rsp->gp_flags); } /* * Dump stacks of all tasks running on stalled CPUs. */ static void rcu_dump_cpu_stacks(struct rcu_state *rsp) { int cpu; unsigned long flags; struct rcu_node *rnp; rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); if (rnp->qsmask != 0) { for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) if (rnp->qsmask & (1UL << cpu)) dump_cpu_task(rnp->grplo + cpu); } raw_spin_unlock_irqrestore(&rnp->lock, flags); } } static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum) { int cpu; long delta; unsigned long flags; unsigned long gpa; unsigned long j; int ndetected = 0; struct rcu_node *rnp = rcu_get_root(rsp); long totqlen = 0; /* Only let one CPU complain about others per time interval. */ raw_spin_lock_irqsave(&rnp->lock, flags); delta = jiffies - READ_ONCE(rsp->jiffies_stall); if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } WRITE_ONCE(rsp->jiffies_stall, jiffies + 3 * rcu_jiffies_till_stall_check() + 3); raw_spin_unlock_irqrestore(&rnp->lock, flags); /* * OK, time to rat on our buddy... * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ pr_err("INFO: %s detected stalls on CPUs/tasks:", rsp->name); print_cpu_stall_info_begin(); rcu_for_each_leaf_node(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); ndetected += rcu_print_task_stall(rnp); if (rnp->qsmask != 0) { for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++) if (rnp->qsmask & (1UL << cpu)) { print_cpu_stall_info(rsp, rnp->grplo + cpu); ndetected++; } } raw_spin_unlock_irqrestore(&rnp->lock, flags); } print_cpu_stall_info_end(); for_each_possible_cpu(cpu) totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen; pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n", smp_processor_id(), (long)(jiffies - rsp->gp_start), (long)rsp->gpnum, (long)rsp->completed, totqlen); if (ndetected) { rcu_dump_cpu_stacks(rsp); } else { if (READ_ONCE(rsp->gpnum) != gpnum || READ_ONCE(rsp->completed) == gpnum) { pr_err("INFO: Stall ended before state dump start\n"); } else { j = jiffies; gpa = READ_ONCE(rsp->gp_activity); pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n", rsp->name, j - gpa, j, gpa, jiffies_till_next_fqs, rcu_get_root(rsp)->qsmask); /* In this case, the current CPU might be at fault. */ sched_show_task(current); } } /* Complain about tasks blocking the grace period. */ rcu_print_detail_task_stall(rsp); rcu_check_gp_kthread_starvation(rsp); force_quiescent_state(rsp); /* Kick them all. */ } static void print_cpu_stall(struct rcu_state *rsp) { int cpu; unsigned long flags; struct rcu_node *rnp = rcu_get_root(rsp); long totqlen = 0; /* * OK, time to rat on ourselves... * See Documentation/RCU/stallwarn.txt for info on how to debug * RCU CPU stall warnings. */ pr_err("INFO: %s self-detected stall on CPU", rsp->name); print_cpu_stall_info_begin(); print_cpu_stall_info(rsp, smp_processor_id()); print_cpu_stall_info_end(); for_each_possible_cpu(cpu) totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen; pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n", jiffies - rsp->gp_start, (long)rsp->gpnum, (long)rsp->completed, totqlen); rcu_check_gp_kthread_starvation(rsp); rcu_dump_cpu_stacks(rsp); raw_spin_lock_irqsave(&rnp->lock, flags); if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall))) WRITE_ONCE(rsp->jiffies_stall, jiffies + 3 * rcu_jiffies_till_stall_check() + 3); raw_spin_unlock_irqrestore(&rnp->lock, flags); /* * Attempt to revive the RCU machinery by forcing a context switch. * * A context switch would normally allow the RCU state machine to make * progress and it could be we're stuck in kernel space without context * switches for an entirely unreasonable amount of time. */ resched_cpu(smp_processor_id()); } static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long completed; unsigned long gpnum; unsigned long gps; unsigned long j; unsigned long js; struct rcu_node *rnp; if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp)) return; j = jiffies; /* * Lots of memory barriers to reject false positives. * * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall, * then rsp->gp_start, and finally rsp->completed. These values * are updated in the opposite order with memory barriers (or * equivalent) during grace-period initialization and cleanup. * Now, a false positive can occur if we get an new value of * rsp->gp_start and a old value of rsp->jiffies_stall. But given * the memory barriers, the only way that this can happen is if one * grace period ends and another starts between these two fetches. * Detect this by comparing rsp->completed with the previous fetch * from rsp->gpnum. * * Given this check, comparisons of jiffies, rsp->jiffies_stall, * and rsp->gp_start suffice to forestall false positives. */ gpnum = READ_ONCE(rsp->gpnum); smp_rmb(); /* Pick up ->gpnum first... */ js = READ_ONCE(rsp->jiffies_stall); smp_rmb(); /* ...then ->jiffies_stall before the rest... */ gps = READ_ONCE(rsp->gp_start); smp_rmb(); /* ...and finally ->gp_start before ->completed. */ completed = READ_ONCE(rsp->completed); if (ULONG_CMP_GE(completed, gpnum) || ULONG_CMP_LT(j, js) || ULONG_CMP_GE(gps, js)) return; /* No stall or GP completed since entering function. */ rnp = rdp->mynode; if (rcu_gp_in_progress(rsp) && (READ_ONCE(rnp->qsmask) & rdp->grpmask)) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rsp); } else if (rcu_gp_in_progress(rsp) && ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) { /* They had a few time units to dump stack, so complain. */ print_other_cpu_stall(rsp, gpnum); } } /** * rcu_cpu_stall_reset - prevent further stall warnings in current grace period * * Set the stall-warning timeout way off into the future, thus preventing * any RCU CPU stall-warning messages from appearing in the current set of * RCU grace periods. * * The caller must disable hard irqs. */ void rcu_cpu_stall_reset(void) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2); } /* * Initialize the specified rcu_data structure's default callback list * to empty. The default callback list is the one that is not used by * no-callbacks CPUs. */ static void init_default_callback_list(struct rcu_data *rdp) { int i; rdp->nxtlist = NULL; for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; } /* * Initialize the specified rcu_data structure's callback list to empty. */ static void init_callback_list(struct rcu_data *rdp) { if (init_nocb_callback_list(rdp)) return; init_default_callback_list(rdp); } /* * Determine the value that ->completed will have at the end of the * next subsequent grace period. This is used to tag callbacks so that * a CPU can invoke callbacks in a timely fashion even if that CPU has * been dyntick-idle for an extended period with callbacks under the * influence of RCU_FAST_NO_HZ. * * The caller must hold rnp->lock with interrupts disabled. */ static unsigned long rcu_cbs_completed(struct rcu_state *rsp, struct rcu_node *rnp) { /* * If RCU is idle, we just wait for the next grace period. * But we can only be sure that RCU is idle if we are looking * at the root rcu_node structure -- otherwise, a new grace * period might have started, but just not yet gotten around * to initializing the current non-root rcu_node structure. */ if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed) return rnp->completed + 1; /* * Otherwise, wait for a possible partial grace period and * then the subsequent full grace period. */ return rnp->completed + 2; } /* * Trace-event helper function for rcu_start_future_gp() and * rcu_nocb_wait_gp(). */ static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, unsigned long c, const char *s) { trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum, rnp->completed, c, rnp->level, rnp->grplo, rnp->grphi, s); } /* * Start some future grace period, as needed to handle newly arrived * callbacks. The required future grace periods are recorded in each * rcu_node structure's ->need_future_gp field. Returns true if there * is reason to awaken the grace-period kthread. * * The caller must hold the specified rcu_node structure's ->lock. */ static bool __maybe_unused rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp, unsigned long *c_out) { unsigned long c; int i; bool ret = false; struct rcu_node *rnp_root = rcu_get_root(rdp->rsp); /* * Pick up grace-period number for new callbacks. If this * grace period is already marked as needed, return to the caller. */ c = rcu_cbs_completed(rdp->rsp, rnp); trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf")); if (rnp->need_future_gp[c & 0x1]) { trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf")); goto out; } /* * If either this rcu_node structure or the root rcu_node structure * believe that a grace period is in progress, then we must wait * for the one following, which is in "c". Because our request * will be noticed at the end of the current grace period, we don't * need to explicitly start one. We only do the lockless check * of rnp_root's fields if the current rcu_node structure thinks * there is no grace period in flight, and because we hold rnp->lock, * the only possible change is when rnp_root's two fields are * equal, in which case rnp_root->gpnum might be concurrently * incremented. But that is OK, as it will just result in our * doing some extra useless work. */ if (rnp->gpnum != rnp->completed || READ_ONCE(rnp_root->gpnum) != READ_ONCE(rnp_root->completed)) { rnp->need_future_gp[c & 0x1]++; trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf")); goto out; } /* * There might be no grace period in progress. If we don't already * hold it, acquire the root rcu_node structure's lock in order to * start one (if needed). */ if (rnp != rnp_root) { raw_spin_lock(&rnp_root->lock); smp_mb__after_unlock_lock(); } /* * Get a new grace-period number. If there really is no grace * period in progress, it will be smaller than the one we obtained * earlier. Adjust callbacks as needed. Note that even no-CBs * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed. */ c = rcu_cbs_completed(rdp->rsp, rnp_root); for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++) if (ULONG_CMP_LT(c, rdp->nxtcompleted[i])) rdp->nxtcompleted[i] = c; /* * If the needed for the required grace period is already * recorded, trace and leave. */ if (rnp_root->need_future_gp[c & 0x1]) { trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot")); goto unlock_out; } /* Record the need for the future grace period. */ rnp_root->need_future_gp[c & 0x1]++; /* If a grace period is not already in progress, start one. */ if (rnp_root->gpnum != rnp_root->completed) { trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot")); } else { trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot")); ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp); } unlock_out: if (rnp != rnp_root) raw_spin_unlock(&rnp_root->lock); out: if (c_out != NULL) *c_out = c; return ret; } /* * Clean up any old requests for the just-ended grace period. Also return * whether any additional grace periods have been requested. Also invoke * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads * waiting for this grace period to complete. */ static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp) { int c = rnp->completed; int needmore; struct rcu_data *rdp = this_cpu_ptr(rsp->rda); rcu_nocb_gp_cleanup(rsp, rnp); rnp->need_future_gp[c & 0x1] = 0; needmore = rnp->need_future_gp[(c + 1) & 0x1]; trace_rcu_future_gp(rnp, rdp, c, needmore ? TPS("CleanupMore") : TPS("Cleanup")); return needmore; } /* * Awaken the grace-period kthread for the specified flavor of RCU. * Don't do a self-awaken, and don't bother awakening when there is * nothing for the grace-period kthread to do (as in several CPUs * raced to awaken, and we lost), and finally don't try to awaken * a kthread that has not yet been created. */ static void rcu_gp_kthread_wake(struct rcu_state *rsp) { if (current == rsp->gp_kthread || !READ_ONCE(rsp->gp_flags) || !rsp->gp_kthread) return; wake_up(&rsp->gp_wq); } /* * If there is room, assign a ->completed number to any callbacks on * this CPU that have not already been assigned. Also accelerate any * callbacks that were previously assigned a ->completed number that has * since proven to be too conservative, which can happen if callbacks get * assigned a ->completed number while RCU is idle, but with reference to * a non-root rcu_node structure. This function is idempotent, so it does * not hurt to call it repeatedly. Returns an flag saying that we should * awaken the RCU grace-period kthread. * * The caller must hold rnp->lock with interrupts disabled. */ static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { unsigned long c; int i; bool ret; /* If the CPU has no callbacks, nothing to do. */ if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL]) return false; /* * Starting from the sublist containing the callbacks most * recently assigned a ->completed number and working down, find the * first sublist that is not assignable to an upcoming grace period. * Such a sublist has something in it (first two tests) and has * a ->completed number assigned that will complete sooner than * the ->completed number for newly arrived callbacks (last test). * * The key point is that any later sublist can be assigned the * same ->completed number as the newly arrived callbacks, which * means that the callbacks in any of these later sublist can be * grouped into a single sublist, whether or not they have already * been assigned a ->completed number. */ c = rcu_cbs_completed(rsp, rnp); for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--) if (rdp->nxttail[i] != rdp->nxttail[i - 1] && !ULONG_CMP_GE(rdp->nxtcompleted[i], c)) break; /* * If there are no sublist for unassigned callbacks, leave. * At the same time, advance "i" one sublist, so that "i" will * index into the sublist where all the remaining callbacks should * be grouped into. */ if (++i >= RCU_NEXT_TAIL) return false; /* * Assign all subsequent callbacks' ->completed number to the next * full grace period and group them all in the sublist initially * indexed by "i". */ for (; i <= RCU_NEXT_TAIL; i++) { rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL]; rdp->nxtcompleted[i] = c; } /* Record any needed additional grace periods. */ ret = rcu_start_future_gp(rnp, rdp, NULL); /* Trace depending on how much we were able to accelerate. */ if (!*rdp->nxttail[RCU_WAIT_TAIL]) trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB")); else trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB")); return ret; } /* * Move any callbacks whose grace period has completed to the * RCU_DONE_TAIL sublist, then compact the remaining sublists and * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL * sublist. This function is idempotent, so it does not hurt to * invoke it repeatedly. As long as it is not invoked -too- often... * Returns true if the RCU grace-period kthread needs to be awakened. * * The caller must hold rnp->lock with interrupts disabled. */ static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { int i, j; /* If the CPU has no callbacks, nothing to do. */ if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL]) return false; /* * Find all callbacks whose ->completed numbers indicate that they * are ready to invoke, and put them into the RCU_DONE_TAIL sublist. */ for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) { if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i])) break; rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i]; } /* Clean up any sublist tail pointers that were misordered above. */ for (j = RCU_WAIT_TAIL; j < i; j++) rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL]; /* Copy down callbacks to fill in empty sublists. */ for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) { if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL]) break; rdp->nxttail[j] = rdp->nxttail[i]; rdp->nxtcompleted[j] = rdp->nxtcompleted[i]; } /* Classify any remaining callbacks. */ return rcu_accelerate_cbs(rsp, rnp, rdp); } /* * Update CPU-local rcu_data state to record the beginnings and ends of * grace periods. The caller must hold the ->lock of the leaf rcu_node * structure corresponding to the current CPU, and must have irqs disabled. * Returns true if the grace-period kthread needs to be awakened. */ static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { bool ret; /* Handle the ends of any preceding grace periods first. */ if (rdp->completed == rnp->completed && !unlikely(READ_ONCE(rdp->gpwrap))) { /* No grace period end, so just accelerate recent callbacks. */ ret = rcu_accelerate_cbs(rsp, rnp, rdp); } else { /* Advance callbacks. */ ret = rcu_advance_cbs(rsp, rnp, rdp); /* Remember that we saw this grace-period completion. */ rdp->completed = rnp->completed; trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend")); } if (rdp->gpnum != rnp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) { /* * If the current grace period is waiting for this CPU, * set up to detect a quiescent state, otherwise don't * go looking for one. */ rdp->gpnum = rnp->gpnum; trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart")); rdp->passed_quiesce = 0; rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr); rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask); zero_cpu_stall_ticks(rdp); WRITE_ONCE(rdp->gpwrap, false); } return ret; } static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; bool needwake; struct rcu_node *rnp; local_irq_save(flags); rnp = rdp->mynode; if ((rdp->gpnum == READ_ONCE(rnp->gpnum) && rdp->completed == READ_ONCE(rnp->completed) && !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */ !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */ local_irq_restore(flags); return; } smp_mb__after_unlock_lock(); needwake = __note_gp_changes(rsp, rnp, rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); if (needwake) rcu_gp_kthread_wake(rsp); } static void rcu_gp_slow(struct rcu_state *rsp, int delay) { if (delay > 0 && !(rsp->gpnum % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) schedule_timeout_uninterruptible(delay); } /* * Initialize a new grace period. Return 0 if no grace period required. */ static int rcu_gp_init(struct rcu_state *rsp) { unsigned long oldmask; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(rsp); WRITE_ONCE(rsp->gp_activity, jiffies); raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); if (!READ_ONCE(rsp->gp_flags)) { /* Spurious wakeup, tell caller to go back to sleep. */ raw_spin_unlock_irq(&rnp->lock); return 0; } WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */ if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) { /* * Grace period already in progress, don't start another. * Not supposed to be able to happen. */ raw_spin_unlock_irq(&rnp->lock); return 0; } /* Advance to a new grace period and initialize state. */ record_gp_stall_check_time(rsp); /* Record GP times before starting GP, hence smp_store_release(). */ smp_store_release(&rsp->gpnum, rsp->gpnum + 1); trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start")); raw_spin_unlock_irq(&rnp->lock); /* * Apply per-leaf buffered online and offline operations to the * rcu_node tree. Note that this new grace period need not wait * for subsequent online CPUs, and that quiescent-state forcing * will handle subsequent offline CPUs. */ rcu_for_each_leaf_node(rsp, rnp) { rcu_gp_slow(rsp, gp_preinit_delay); raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); if (rnp->qsmaskinit == rnp->qsmaskinitnext && !rnp->wait_blkd_tasks) { /* Nothing to do on this leaf rcu_node structure. */ raw_spin_unlock_irq(&rnp->lock); continue; } /* Record old state, apply changes to ->qsmaskinit field. */ oldmask = rnp->qsmaskinit; rnp->qsmaskinit = rnp->qsmaskinitnext; /* If zero-ness of ->qsmaskinit changed, propagate up tree. */ if (!oldmask != !rnp->qsmaskinit) { if (!oldmask) /* First online CPU for this rcu_node. */ rcu_init_new_rnp(rnp); else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */ rnp->wait_blkd_tasks = true; else /* Last offline CPU and can propagate. */ rcu_cleanup_dead_rnp(rnp); } /* * If all waited-on tasks from prior grace period are * done, and if all this rcu_node structure's CPUs are * still offline, propagate up the rcu_node tree and * clear ->wait_blkd_tasks. Otherwise, if one of this * rcu_node structure's CPUs has since come back online, * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp() * checks for this, so just call it unconditionally). */ if (rnp->wait_blkd_tasks && (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) { rnp->wait_blkd_tasks = false; rcu_cleanup_dead_rnp(rnp); } raw_spin_unlock_irq(&rnp->lock); } /* * Set the quiescent-state-needed bits in all the rcu_node * structures for all currently online CPUs in breadth-first order, * starting from the root rcu_node structure, relying on the layout * of the tree within the rsp->node[] array. Note that other CPUs * will access only the leaves of the hierarchy, thus seeing that no * grace period is in progress, at least until the corresponding * leaf node has been initialized. In addition, we have excluded * CPU-hotplug operations. * * The grace period cannot complete until the initialization * process finishes, because this kthread handles both. */ rcu_for_each_node_breadth_first(rsp, rnp) { rcu_gp_slow(rsp, gp_init_delay); raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); rdp = this_cpu_ptr(rsp->rda); rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; WRITE_ONCE(rnp->gpnum, rsp->gpnum); if (WARN_ON_ONCE(rnp->completed != rsp->completed)) WRITE_ONCE(rnp->completed, rsp->completed); if (rnp == rdp->mynode) (void)__note_gp_changes(rsp, rnp, rdp); rcu_preempt_boost_start_gp(rnp); trace_rcu_grace_period_init(rsp->name, rnp->gpnum, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); raw_spin_unlock_irq(&rnp->lock); cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); } return 1; } /* * Do one round of quiescent-state forcing. */ static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in) { int fqs_state = fqs_state_in; bool isidle = false; unsigned long maxj; struct rcu_node *rnp = rcu_get_root(rsp); WRITE_ONCE(rsp->gp_activity, jiffies); rsp->n_force_qs++; if (fqs_state == RCU_SAVE_DYNTICK) { /* Collect dyntick-idle snapshots. */ if (is_sysidle_rcu_state(rsp)) { isidle = true; maxj = jiffies - ULONG_MAX / 4; } force_qs_rnp(rsp, dyntick_save_progress_counter, &isidle, &maxj); rcu_sysidle_report_gp(rsp, isidle, maxj); fqs_state = RCU_FORCE_QS; } else { /* Handle dyntick-idle and offline CPUs. */ isidle = true; force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj); } /* Clear flag to prevent immediate re-entry. */ if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS); raw_spin_unlock_irq(&rnp->lock); } return fqs_state; } /* * Clean up after the old grace period. */ static void rcu_gp_cleanup(struct rcu_state *rsp) { unsigned long gp_duration; bool needgp = false; int nocb = 0; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(rsp); WRITE_ONCE(rsp->gp_activity, jiffies); raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); gp_duration = jiffies - rsp->gp_start; if (gp_duration > rsp->gp_max) rsp->gp_max = gp_duration; /* * We know the grace period is complete, but to everyone else * it appears to still be ongoing. But it is also the case * that to everyone else it looks like there is nothing that * they can do to advance the grace period. It is therefore * safe for us to drop the lock in order to mark the grace * period as completed in all of the rcu_node structures. */ raw_spin_unlock_irq(&rnp->lock); /* * Propagate new ->completed value to rcu_node structures so * that other CPUs don't have to wait until the start of the next * grace period to process their callbacks. This also avoids * some nasty RCU grace-period initialization races by forcing * the end of the current grace period to be completely recorded in * all of the rcu_node structures before the beginning of the next * grace period is recorded in any of the rcu_node structures. */ rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); WARN_ON_ONCE(rnp->qsmask); WRITE_ONCE(rnp->completed, rsp->gpnum); rdp = this_cpu_ptr(rsp->rda); if (rnp == rdp->mynode) needgp = __note_gp_changes(rsp, rnp, rdp) || needgp; /* smp_mb() provided by prior unlock-lock pair. */ nocb += rcu_future_gp_cleanup(rsp, rnp); raw_spin_unlock_irq(&rnp->lock); cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); rcu_gp_slow(rsp, gp_cleanup_delay); } rnp = rcu_get_root(rsp); raw_spin_lock_irq(&rnp->lock); smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */ rcu_nocb_gp_set(rnp, nocb); /* Declare grace period done. */ WRITE_ONCE(rsp->completed, rsp->gpnum); trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end")); rsp->fqs_state = RCU_GP_IDLE; rdp = this_cpu_ptr(rsp->rda); /* Advance CBs to reduce false positives below. */ needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp; if (needgp || cpu_needs_another_gp(rsp, rdp)) { WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("newreq")); } raw_spin_unlock_irq(&rnp->lock); } /* * Body of kthread that handles grace periods. */ static int __noreturn rcu_gp_kthread(void *arg) { int fqs_state; int gf; unsigned long j; int ret; struct rcu_state *rsp = arg; struct rcu_node *rnp = rcu_get_root(rsp); rcu_bind_gp_kthread(); for (;;) { /* Handle grace-period start. */ for (;;) { trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("reqwait")); rsp->gp_state = RCU_GP_WAIT_GPS; wait_event_interruptible(rsp->gp_wq, READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_INIT); /* Locking provides needed memory barrier. */ if (rcu_gp_init(rsp)) break; cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); WARN_ON(signal_pending(current)); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("reqwaitsig")); } /* Handle quiescent-state forcing. */ fqs_state = RCU_SAVE_DYNTICK; j = jiffies_till_first_fqs; if (j > HZ) { j = HZ; jiffies_till_first_fqs = HZ; } ret = 0; for (;;) { if (!ret) rsp->jiffies_force_qs = jiffies + j; trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("fqswait")); rsp->gp_state = RCU_GP_WAIT_FQS; ret = wait_event_interruptible_timeout(rsp->gp_wq, ((gf = READ_ONCE(rsp->gp_flags)) & RCU_GP_FLAG_FQS) || (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)), j); /* Locking provides needed memory barriers. */ /* If grace period done, leave loop. */ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) break; /* If time for quiescent-state forcing, do it. */ if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) || (gf & RCU_GP_FLAG_FQS)) { trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("fqsstart")); fqs_state = rcu_gp_fqs(rsp, fqs_state); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("fqsend")); cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); } else { /* Deal with stray signal. */ cond_resched_rcu_qs(); WRITE_ONCE(rsp->gp_activity, jiffies); WARN_ON(signal_pending(current)); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("fqswaitsig")); } j = jiffies_till_next_fqs; if (j > HZ) { j = HZ; jiffies_till_next_fqs = HZ; } else if (j < 1) { j = 1; jiffies_till_next_fqs = 1; } } /* Handle grace-period end. */ rcu_gp_cleanup(rsp); } } /* * Start a new RCU grace period if warranted, re-initializing the hierarchy * in preparation for detecting the next grace period. The caller must hold * the root node's ->lock and hard irqs must be disabled. * * Note that it is legal for a dying CPU (which is marked as offline) to * invoke this function. This can happen when the dying CPU reports its * quiescent state. * * Returns true if the grace-period kthread must be awakened. */ static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) { /* * Either we have not yet spawned the grace-period * task, this CPU does not need another grace period, * or a grace period is already in progress. * Either way, don't start a new grace period. */ return false; } WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT); trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gpnum), TPS("newreq")); /* * We can't do wakeups while holding the rnp->lock, as that * could cause possible deadlocks with the rq->lock. Defer * the wakeup to our caller. */ return true; } /* * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's * callbacks. Note that rcu_start_gp_advanced() cannot do this because it * is invoked indirectly from rcu_advance_cbs(), which would result in * endless recursion -- or would do so if it wasn't for the self-deadlock * that is encountered beforehand. * * Returns true if the grace-period kthread needs to be awakened. */ static bool rcu_start_gp(struct rcu_state *rsp) { struct rcu_data *rdp = this_cpu_ptr(rsp->rda); struct rcu_node *rnp = rcu_get_root(rsp); bool ret = false; /* * If there is no grace period in progress right now, any * callbacks we have up to this point will be satisfied by the * next grace period. Also, advancing the callbacks reduces the * probability of false positives from cpu_needs_another_gp() * resulting in pointless grace periods. So, advance callbacks * then start the grace period! */ ret = rcu_advance_cbs(rsp, rnp, rdp) || ret; ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret; return ret; } /* * Report a full set of quiescent states to the specified rcu_state * data structure. This involves cleaning up after the prior grace * period and letting rcu_start_gp() start up the next grace period * if one is needed. Note that the caller must hold rnp->lock, which * is released before return. */ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) __releases(rcu_get_root(rsp)->lock) { WARN_ON_ONCE(!rcu_gp_in_progress(rsp)); WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); rcu_gp_kthread_wake(rsp); } /* * Similar to rcu_report_qs_rdp(), for which it is a helper function. * Allows quiescent states for a group of CPUs to be reported at one go * to the specified rcu_node structure, though all the CPUs in the group * must be represented by the same rcu_node structure (which need not be a * leaf rcu_node structure, though it often will be). The gps parameter * is the grace-period snapshot, which means that the quiescent states * are valid only if rnp->gpnum is equal to gps. That structure's lock * must be held upon entry, and it is released before return. */ static void rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp, unsigned long gps, unsigned long flags) __releases(rnp->lock) { unsigned long oldmask = 0; struct rcu_node *rnp_c; /* Walk up the rcu_node hierarchy. */ for (;;) { if (!(rnp->qsmask & mask) || rnp->gpnum != gps) { /* * Our bit has already been cleared, or the * relevant grace period is already over, so done. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ rnp->qsmask &= ~mask; trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum, mask, rnp->qsmask, rnp->level, rnp->grplo, rnp->grphi, !!rnp->gp_tasks); if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { /* Other bits still set at this level, so done. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rnp->grpmask; if (rnp->parent == NULL) { /* No more levels. Exit loop holding root lock. */ break; } raw_spin_unlock_irqrestore(&rnp->lock, flags); rnp_c = rnp; rnp = rnp->parent; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); oldmask = rnp_c->qsmask; } /* * Get here if we are the last CPU to pass through a quiescent * state for this grace period. Invoke rcu_report_qs_rsp() * to clean up and start the next grace period if one is needed. */ rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */ } /* * Record a quiescent state for all tasks that were previously queued * on the specified rcu_node structure and that were blocking the current * RCU grace period. The caller must hold the specified rnp->lock with * irqs disabled, and this lock is released upon return, but irqs remain * disabled. */ static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp, struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock) { unsigned long gps; unsigned long mask; struct rcu_node *rnp_p; if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p || rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; /* Still need more quiescent states! */ } rnp_p = rnp->parent; if (rnp_p == NULL) { /* * Only one rcu_node structure in the tree, so don't * try to report up to its nonexistent parent! */ rcu_report_qs_rsp(rsp, flags); return; } /* Report up the rest of the hierarchy, tracking current ->gpnum. */ gps = rnp->gpnum; mask = rnp->grpmask; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ smp_mb__after_unlock_lock(); rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags); } /* * Record a quiescent state for the specified CPU to that CPU's rcu_data * structure. This must be either called from the specified CPU, or * called when the specified CPU is known to be offline (and when it is * also known that no other CPU is concurrently trying to help the offline * CPU). The lastcomp argument is used to make sure we are still in the * grace period of interest. We don't want to end the current grace period * based on quiescent states detected in an earlier grace period! */ static void rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; unsigned long mask; bool needwake; struct rcu_node *rnp; rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); if ((rdp->passed_quiesce == 0 && rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) || rdp->gpnum != rnp->gpnum || rnp->completed == rnp->gpnum || rdp->gpwrap) { /* * The grace period in which this quiescent state was * recorded has ended, so don't report it upwards. * We will instead need a new quiescent state that lies * within the current grace period. */ rdp->passed_quiesce = 0; /* need qs for new gp. */ rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_qs_ctr); raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } mask = rdp->grpmask; if ((rnp->qsmask & mask) == 0) { raw_spin_unlock_irqrestore(&rnp->lock, flags); } else { rdp->qs_pending = 0; /* * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. */ needwake = rcu_accelerate_cbs(rsp, rnp, rdp); rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); /* ^^^ Released rnp->lock */ if (needwake) rcu_gp_kthread_wake(rsp); } } /* * Check to see if there is a new grace period of which this CPU * is not yet aware, and if so, set up local rcu_data state for it. * Otherwise, see if this CPU has just passed through its first * quiescent state for this grace period, and record that fact if so. */ static void rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp) { /* Check for grace-period ends and beginnings. */ note_gp_changes(rsp, rdp); /* * Does this CPU still need to do its part for current grace period? * If no, return and let the other CPUs do their part as well. */ if (!rdp->qs_pending) return; /* * Was there a quiescent state since the beginning of the grace * period? If no, then exit and wait for the next call. */ if (!rdp->passed_quiesce && rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) return; /* * Tell RCU we are done (but rcu_report_qs_rdp() will be the * judge of that). */ rcu_report_qs_rdp(rdp->cpu, rsp, rdp); } /* * Send the specified CPU's RCU callbacks to the orphanage. The * specified CPU must be offline, and the caller must hold the * ->orphan_lock. */ static void rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { /* No-CBs CPUs do not have orphanable callbacks. */ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_is_nocb_cpu(rdp->cpu)) return; /* * Orphan the callbacks. First adjust the counts. This is safe * because _rcu_barrier() excludes CPU-hotplug operations, so it * cannot be running now. Thus no memory barrier is required. */ if (rdp->nxtlist != NULL) { rsp->qlen_lazy += rdp->qlen_lazy; rsp->qlen += rdp->qlen; rdp->n_cbs_orphaned += rdp->qlen; rdp->qlen_lazy = 0; WRITE_ONCE(rdp->qlen, 0); } /* * Next, move those callbacks still needing a grace period to * the orphanage, where some other CPU will pick them up. * Some of the callbacks might have gone partway through a grace * period, but that is too bad. They get to start over because we * cannot assume that grace periods are synchronized across CPUs. * We don't bother updating the ->nxttail[] array yet, instead * we just reset the whole thing later on. */ if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) { *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL]; rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; } /* * Then move the ready-to-invoke callbacks to the orphanage, * where some other CPU will pick them up. These will not be * required to pass though another grace period: They are done. */ if (rdp->nxtlist != NULL) { *rsp->orphan_donetail = rdp->nxtlist; rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL]; } /* * Finally, initialize the rcu_data structure's list to empty and * disallow further callbacks on this CPU. */ init_callback_list(rdp); rdp->nxttail[RCU_NEXT_TAIL] = NULL; } /* * Adopt the RCU callbacks from the specified rcu_state structure's * orphanage. The caller must hold the ->orphan_lock. */ static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags) { int i; struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); /* No-CBs CPUs are handled specially. */ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags)) return; /* Do the accounting first. */ rdp->qlen_lazy += rsp->qlen_lazy; rdp->qlen += rsp->qlen; rdp->n_cbs_adopted += rsp->qlen; if (rsp->qlen_lazy != rsp->qlen) rcu_idle_count_callbacks_posted(); rsp->qlen_lazy = 0; rsp->qlen = 0; /* * We do not need a memory barrier here because the only way we * can get here if there is an rcu_barrier() in flight is if * we are the task doing the rcu_barrier(). */ /* First adopt the ready-to-invoke callbacks. */ if (rsp->orphan_donelist != NULL) { *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist; for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--) if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) rdp->nxttail[i] = rsp->orphan_donetail; rsp->orphan_donelist = NULL; rsp->orphan_donetail = &rsp->orphan_donelist; } /* And then adopt the callbacks that still need a grace period. */ if (rsp->orphan_nxtlist != NULL) { *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist; rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail; rsp->orphan_nxtlist = NULL; rsp->orphan_nxttail = &rsp->orphan_nxtlist; } } /* * Trace the fact that this CPU is going offline. */ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp) { RCU_TRACE(unsigned long mask); RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda)); RCU_TRACE(struct rcu_node *rnp = rdp->mynode); if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return; RCU_TRACE(mask = rdp->grpmask); trace_rcu_grace_period(rsp->name, rnp->gpnum + 1 - !!(rnp->qsmask & mask), TPS("cpuofl")); } /* * All CPUs for the specified rcu_node structure have gone offline, * and all tasks that were preempted within an RCU read-side critical * section while running on one of those CPUs have since exited their RCU * read-side critical section. Some other CPU is reporting this fact with * the specified rcu_node structure's ->lock held and interrupts disabled. * This function therefore goes up the tree of rcu_node structures, * clearing the corresponding bits in the ->qsmaskinit fields. Note that * the leaf rcu_node structure's ->qsmaskinit field has already been * updated * * This function does check that the specified rcu_node structure has * all CPUs offline and no blocked tasks, so it is OK to invoke it * prematurely. That said, invoking it after the fact will cost you * a needless lock acquisition. So once it has done its work, don't * invoke it again. */ static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf) { long mask; struct rcu_node *rnp = rnp_leaf; if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || rnp->qsmaskinit || rcu_preempt_has_tasks(rnp)) return; for (;;) { mask = rnp->grpmask; rnp = rnp->parent; if (!rnp) break; raw_spin_lock(&rnp->lock); /* irqs already disabled. */ smp_mb__after_unlock_lock(); /* GP memory ordering. */ rnp->qsmaskinit &= ~mask; rnp->qsmask &= ~mask; if (rnp->qsmaskinit) { raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ return; } raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } } /* * The CPU is exiting the idle loop into the arch_cpu_idle_dead() * function. We now remove it from the rcu_node tree's ->qsmaskinit * bit masks. */ static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp) { unsigned long flags; unsigned long mask; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return; /* Remove outgoing CPU from mask in the leaf rcu_node structure. */ mask = rdp->grpmask; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); /* Enforce GP memory-order guarantee. */ rnp->qsmaskinitnext &= ~mask; raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * The CPU has been completely removed, and some other CPU is reporting * this fact from process context. Do the remainder of the cleanup, * including orphaning the outgoing CPU's RCU callbacks, and also * adopting them. There can only be one CPU hotplug operation at a time, * so no other CPU can be attempting to update rcu_cpu_kthread_task. */ static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp) { unsigned long flags; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */ if (!IS_ENABLED(CONFIG_HOTPLUG_CPU)) return; /* Adjust any no-longer-needed kthreads. */ rcu_boost_kthread_setaffinity(rnp, -1); /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */ raw_spin_lock_irqsave(&rsp->orphan_lock, flags); rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp); rcu_adopt_orphan_cbs(rsp, flags); raw_spin_unlock_irqrestore(&rsp->orphan_lock, flags); WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL, "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n", cpu, rdp->qlen, rdp->nxtlist); } /* * Invoke any RCU callbacks that have made it to the end of their grace * period. Thottle as specified by rdp->blimit. */ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) { unsigned long flags; struct rcu_head *next, *list, **tail; long bl, count, count_lazy; int i; /* If no callbacks are ready, just return. */ if (!cpu_has_callbacks_ready_to_invoke(rdp)) { trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0); trace_rcu_batch_end(rsp->name, 0, !!READ_ONCE(rdp->nxtlist), need_resched(), is_idle_task(current), rcu_is_callbacks_kthread()); return; } /* * Extract the list of ready callbacks, disabling to prevent * races with call_rcu() from interrupt handlers. */ local_irq_save(flags); WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); bl = rdp->blimit; trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl); list = rdp->nxtlist; rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL]; *rdp->nxttail[RCU_DONE_TAIL] = NULL; tail = rdp->nxttail[RCU_DONE_TAIL]; for (i = RCU_NEXT_SIZE - 1; i >= 0; i--) if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL]) rdp->nxttail[i] = &rdp->nxtlist; local_irq_restore(flags); /* Invoke callbacks. */ count = count_lazy = 0; while (list) { next = list->next; prefetch(next); debug_rcu_head_unqueue(list); if (__rcu_reclaim(rsp->name, list)) count_lazy++; list = next; /* Stop only if limit reached and CPU has something to do. */ if (++count >= bl && (need_resched() || (!is_idle_task(current) && !rcu_is_callbacks_kthread()))) break; } local_irq_save(flags); trace_rcu_batch_end(rsp->name, count, !!list, need_resched(), is_idle_task(current), rcu_is_callbacks_kthread()); /* Update count, and requeue any remaining callbacks. */ if (list != NULL) { *tail = rdp->nxtlist; rdp->nxtlist = list; for (i = 0; i < RCU_NEXT_SIZE; i++) if (&rdp->nxtlist == rdp->nxttail[i]) rdp->nxttail[i] = tail; else break; } smp_mb(); /* List handling before counting for rcu_barrier(). */ rdp->qlen_lazy -= count_lazy; WRITE_ONCE(rdp->qlen, rdp->qlen - count); rdp->n_cbs_invoked += count; /* Reinstate batch limit if we have worked down the excess. */ if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark) rdp->blimit = blimit; /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) { rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = rdp->qlen; WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0)); local_irq_restore(flags); /* Re-invoke RCU core processing if there are callbacks remaining. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) invoke_rcu_core(); } /* * Check to see if this CPU is in a non-context-switch quiescent state * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). * Also schedule RCU core processing. * * This function must be called from hardirq context. It is normally * invoked from the scheduling-clock interrupt. If rcu_pending returns * false, there is no point in invoking rcu_check_callbacks(). */ void rcu_check_callbacks(int user) { trace_rcu_utilization(TPS("Start scheduler-tick")); increment_cpu_stall_ticks(); if (user || rcu_is_cpu_rrupt_from_idle()) { /* * Get here if this CPU took its interrupt from user * mode or from the idle loop, and if this is not a * nested interrupt. In this case, the CPU is in * a quiescent state, so note it. * * No memory barrier is required here because both * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local * variables that other CPUs neither access nor modify, * at least not while the corresponding CPU is online. */ rcu_sched_qs(); rcu_bh_qs(); } else if (!in_softirq()) { /* * Get here if this CPU did not take its interrupt from * softirq, in other words, if it is not interrupting * a rcu_bh read-side critical section. This is an _bh * critical section, so note it. */ rcu_bh_qs(); } rcu_preempt_check_callbacks(); if (rcu_pending()) invoke_rcu_core(); if (user) rcu_note_voluntary_context_switch(current); trace_rcu_utilization(TPS("End scheduler-tick")); } /* * Scan the leaf rcu_node structures, processing dyntick state for any that * have not yet encountered a quiescent state, using the function specified. * Also initiate boosting for any threads blocked on the root rcu_node. * * The caller must have suppressed start of new grace periods. */ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp, bool *isidle, unsigned long *maxj), bool *isidle, unsigned long *maxj) { unsigned long bit; int cpu; unsigned long flags; unsigned long mask; struct rcu_node *rnp; rcu_for_each_leaf_node(rsp, rnp) { cond_resched_rcu_qs(); mask = 0; raw_spin_lock_irqsave(&rnp->lock, flags); smp_mb__after_unlock_lock(); if (rnp->qsmask == 0) { if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p || rcu_preempt_blocked_readers_cgp(rnp)) { /* * No point in scanning bits because they * are all zero. But we might need to * priority-boost blocked readers. */ rcu_initiate_boost(rnp, flags); /* rcu_initiate_boost() releases rnp->lock */ continue; } if (rnp->parent && (rnp->parent->qsmask & rnp->grpmask)) { /* * Race between grace-period * initialization and task exiting RCU * read-side critical section: Report. */ rcu_report_unblock_qs_rnp(rsp, rnp, flags); /* rcu_report_unblock_qs_rnp() rlses ->lock */ continue; } } cpu = rnp->grplo; bit = 1; for (; cpu <= rnp->grphi; cpu++, bit <<= 1) { if ((rnp->qsmask & bit) != 0) { if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj)) mask |= bit; } } if (mask != 0) { /* Idle/offline CPUs, report (releases rnp->lock. */ rcu_report_qs_rnp(mask, rsp, rnp, rnp->gpnum, flags); } else { /* Nothing to do here, so just drop the lock. */ raw_spin_unlock_irqrestore(&rnp->lock, flags); } } } /* * Force quiescent states on reluctant CPUs, and also detect which * CPUs are in dyntick-idle mode. */ static void force_quiescent_state(struct rcu_state *rsp) { unsigned long flags; bool ret; struct rcu_node *rnp; struct rcu_node *rnp_old = NULL; /* Funnel through hierarchy to reduce memory contention. */ rnp = __this_cpu_read(rsp->rda->mynode); for (; rnp != NULL; rnp = rnp->parent) { ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) || !raw_spin_trylock(&rnp->fqslock); if (rnp_old != NULL) raw_spin_unlock(&rnp_old->fqslock); if (ret) { rsp->n_force_qs_lh++; return; } rnp_old = rnp; } /* rnp_old == rcu_get_root(rsp), rnp == NULL. */ /* Reached the root of the rcu_node tree, acquire lock. */ raw_spin_lock_irqsave(&rnp_old->lock, flags); smp_mb__after_unlock_lock(); raw_spin_unlock(&rnp_old->fqslock); if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) { rsp->n_force_qs_lh++; raw_spin_unlock_irqrestore(&rnp_old->lock, flags); return; /* Someone beat us to it. */ } WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore(&rnp_old->lock, flags); rcu_gp_kthread_wake(rsp); } /* * This does the RCU core processing work for the specified rcu_state * and rcu_data structures. This may be called only from the CPU to * whom the rdp belongs. */ static void __rcu_process_callbacks(struct rcu_state *rsp) { unsigned long flags; bool needwake; struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); WARN_ON_ONCE(rdp->beenonline == 0); /* Update RCU state based on any recent quiescent states. */ rcu_check_quiescent_state(rsp, rdp); /* Does this CPU require a not-yet-started grace period? */ local_irq_save(flags); if (cpu_needs_another_gp(rsp, rdp)) { raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */ needwake = rcu_start_gp(rsp); raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags); if (needwake) rcu_gp_kthread_wake(rsp); } else { local_irq_restore(flags); } /* If there are callbacks ready, invoke them. */ if (cpu_has_callbacks_ready_to_invoke(rdp)) invoke_rcu_callbacks(rsp, rdp); /* Do any needed deferred wakeups of rcuo kthreads. */ do_nocb_deferred_wakeup(rdp); } /* * Do RCU core processing for the current CPU. */ static void rcu_process_callbacks(struct softirq_action *unused) { struct rcu_state *rsp; if (cpu_is_offline(smp_processor_id())) return; trace_rcu_utilization(TPS("Start RCU core")); for_each_rcu_flavor(rsp) __rcu_process_callbacks(rsp); trace_rcu_utilization(TPS("End RCU core")); } /* * Schedule RCU callback invocation. If the specified type of RCU * does not support RCU priority boosting, just do a direct call, * otherwise wake up the per-CPU kernel kthread. Note that because we * are running on the current CPU with softirqs disabled, the * rcu_cpu_kthread_task cannot disappear out from under us. */ static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp) { if (unlikely(!READ_ONCE(rcu_scheduler_fully_active))) return; if (likely(!rsp->boost)) { rcu_do_batch(rsp, rdp); return; } invoke_rcu_callbacks_kthread(); } static void invoke_rcu_core(void) { if (cpu_online(smp_processor_id())) raise_softirq(RCU_SOFTIRQ); } /* * Handle any core-RCU processing required by a call_rcu() invocation. */ static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp, struct rcu_head *head, unsigned long flags) { bool needwake; /* * If called from an extended quiescent state, invoke the RCU * core in order to force a re-evaluation of RCU's idleness. */ if (!rcu_is_watching()) invoke_rcu_core(); /* If interrupts were disabled or CPU offline, don't invoke RCU core. */ if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) return; /* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke force_quiescent_state() * if some other CPU has recently done so. Also, don't bother * invoking force_quiescent_state() if the newly enqueued callback * is the only one waiting for a grace period to complete. */ if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) { /* Are we ignoring a completed grace period? */ note_gp_changes(rsp, rdp); /* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress(rsp)) { struct rcu_node *rnp_root = rcu_get_root(rsp); raw_spin_lock(&rnp_root->lock); smp_mb__after_unlock_lock(); needwake = rcu_start_gp(rsp); raw_spin_unlock(&rnp_root->lock); if (needwake) rcu_gp_kthread_wake(rsp); } else { /* Give the grace period a kick. */ rdp->blimit = LONG_MAX; if (rsp->n_force_qs == rdp->n_force_qs_snap && *rdp->nxttail[RCU_DONE_TAIL] != head) force_quiescent_state(rsp); rdp->n_force_qs_snap = rsp->n_force_qs; rdp->qlen_last_fqs_check = rdp->qlen; } } } /* * RCU callback function to leak a callback. */ static void rcu_leak_callback(struct rcu_head *rhp) { } /* * Helper function for call_rcu() and friends. The cpu argument will * normally be -1, indicating "currently running CPU". It may specify * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier() * is expected to specify a CPU. */ static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_state *rsp, int cpu, bool lazy) { unsigned long flags; struct rcu_data *rdp; WARN_ON_ONCE((unsigned long)head & 0x1); /* Misaligned rcu_head! */ if (debug_rcu_head_queue(head)) { /* Probable double call_rcu(), so leak the callback. */ WRITE_ONCE(head->func, rcu_leak_callback); WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n"); return; } head->func = func; head->next = NULL; /* * Opportunistically note grace-period endings and beginnings. * Note that we might see a beginning right after we see an * end, but never vice versa, since this CPU has to pass through * a quiescent state betweentimes. */ local_irq_save(flags); rdp = this_cpu_ptr(rsp->rda); /* Add the callback to our list. */ if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) { int offline; if (cpu != -1) rdp = per_cpu_ptr(rsp->rda, cpu); if (likely(rdp->mynode)) { /* Post-boot, so this should be for a no-CBs CPU. */ offline = !__call_rcu_nocb(rdp, head, lazy, flags); WARN_ON_ONCE(offline); /* Offline CPU, _call_rcu() illegal, leak callback. */ local_irq_restore(flags); return; } /* * Very early boot, before rcu_init(). Initialize if needed * and then drop through to queue the callback. */ BUG_ON(cpu != -1); WARN_ON_ONCE(!rcu_is_watching()); if (!likely(rdp->nxtlist)) init_default_callback_list(rdp); } WRITE_ONCE(rdp->qlen, rdp->qlen + 1); if (lazy) rdp->qlen_lazy++; else rcu_idle_count_callbacks_posted(); smp_mb(); /* Count before adding callback for rcu_barrier(). */ *rdp->nxttail[RCU_NEXT_TAIL] = head; rdp->nxttail[RCU_NEXT_TAIL] = &head->next; if (__is_kfree_rcu_offset((unsigned long)func)) trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func, rdp->qlen_lazy, rdp->qlen); else trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen); /* Go handle any RCU core processing required. */ __call_rcu_core(rsp, rdp, head, flags); local_irq_restore(flags); } /* * Queue an RCU-sched callback for invocation after a grace period. */ void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_sched_state, -1, 0); } EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Queue an RCU callback for invocation after a quicker grace period. */ void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_bh_state, -1, 0); } EXPORT_SYMBOL_GPL(call_rcu_bh); /* * Queue an RCU callback for lazy invocation after a grace period. * This will likely be later named something like "call_rcu_lazy()", * but this change will require some way of tagging the lazy RCU * callbacks in the list of pending callbacks. Until then, this * function may only be called from __kfree_rcu(). */ void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, rcu_state_p, -1, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu); /* * Because a context switch is a grace period for RCU-sched and RCU-bh, * any blocking grace-period wait automatically implies a grace period * if there is only one CPU online at any point time during execution * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to * occasionally incorrectly indicate that there are multiple CPUs online * when there was in fact only one the whole time, as this just adds * some overhead: RCU still operates correctly. */ static inline int rcu_blocking_is_gp(void) { int ret; might_sleep(); /* Check for RCU read-side critical section. */ preempt_disable(); ret = num_online_cpus() <= 1; preempt_enable(); return ret; } /** * synchronize_sched - wait until an rcu-sched grace period has elapsed. * * Control will return to the caller some time after a full rcu-sched * grace period has elapsed, in other words after all currently executing * rcu-sched read-side critical sections have completed. These read-side * critical sections are delimited by rcu_read_lock_sched() and * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(), * local_irq_disable(), and so on may be used in place of * rcu_read_lock_sched(). * * This means that all preempt_disable code sequences, including NMI and * non-threaded hardware-interrupt handlers, in progress on entry will * have completed before this primitive returns. However, this does not * guarantee that softirq handlers will have completed, since in some * kernels, these handlers can run in process context, and can block. * * Note that this guarantee implies further memory-ordering guarantees. * On systems with more than one CPU, when synchronize_sched() returns, * each CPU is guaranteed to have executed a full memory barrier since the * end of its last RCU-sched read-side critical section whose beginning * preceded the call to synchronize_sched(). In addition, each CPU having * an RCU read-side critical section that extends beyond the return from * synchronize_sched() is guaranteed to have executed a full memory barrier * after the beginning of synchronize_sched() and before the beginning of * that RCU read-side critical section. Note that these guarantees include * CPUs that are offline, idle, or executing in user mode, as well as CPUs * that are executing in the kernel. * * Furthermore, if CPU A invoked synchronize_sched(), which returned * to its caller on CPU B, then both CPU A and CPU B are guaranteed * to have executed a full memory barrier during the execution of * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but * again only if the system has more than one CPU). * * This primitive provides the guarantees made by the (now removed) * synchronize_kernel() API. In contrast, synchronize_rcu() only * guarantees that rcu_read_lock() sections will have completed. * In "classic RCU", these two guarantees happen to be one and * the same, but can differ in realtime RCU implementations. */ void synchronize_sched(void) { rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && !lock_is_held(&rcu_lock_map) && !lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_sched() in RCU-sched read-side critical section"); if (rcu_blocking_is_gp()) return; if (rcu_gp_is_expedited()) synchronize_sched_expedited(); else wait_rcu_gp(call_rcu_sched); } EXPORT_SYMBOL_GPL(synchronize_sched); /** * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed. * * Control will return to the caller some time after a full rcu_bh grace * period has elapsed, in other words after all currently executing rcu_bh * read-side critical sections have completed. RCU read-side critical * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(), * and may be nested. * * See the description of synchronize_sched() for more detailed information * on memory ordering guarantees. */ void synchronize_rcu_bh(void) { rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) && !lock_is_held(&rcu_lock_map) && !lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section"); if (rcu_blocking_is_gp()) return; if (rcu_gp_is_expedited()) synchronize_rcu_bh_expedited(); else wait_rcu_gp(call_rcu_bh); } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); /** * get_state_synchronize_rcu - Snapshot current RCU state * * Returns a cookie that is used by a later call to cond_synchronize_rcu() * to determine whether or not a full grace period has elapsed in the * meantime. */ unsigned long get_state_synchronize_rcu(void) { /* * Any prior manipulation of RCU-protected data must happen * before the load from ->gpnum. */ smp_mb(); /* ^^^ */ /* * Make sure this load happens before the purportedly * time-consuming work between get_state_synchronize_rcu() * and cond_synchronize_rcu(). */ return smp_load_acquire(&rcu_state_p->gpnum); } EXPORT_SYMBOL_GPL(get_state_synchronize_rcu); /** * cond_synchronize_rcu - Conditionally wait for an RCU grace period * * @oldstate: return value from earlier call to get_state_synchronize_rcu() * * If a full RCU grace period has elapsed since the earlier call to * get_state_synchronize_rcu(), just return. Otherwise, invoke * synchronize_rcu() to wait for a full grace period. * * Yes, this function does not take counter wrap into account. But * counter wrap is harmless. If the counter wraps, we have waited for * more than 2 billion grace periods (and way more on a 64-bit system!), * so waiting for one additional grace period should be just fine. */ void cond_synchronize_rcu(unsigned long oldstate) { unsigned long newstate; /* * Ensure that this load happens before any RCU-destructive * actions the caller might carry out after we return. */ newstate = smp_load_acquire(&rcu_state_p->completed); if (ULONG_CMP_GE(oldstate, newstate)) synchronize_rcu(); } EXPORT_SYMBOL_GPL(cond_synchronize_rcu); static int synchronize_sched_expedited_cpu_stop(void *data) { /* * There must be a full memory barrier on each affected CPU * between the time that try_stop_cpus() is called and the * time that it returns. * * In the current initial implementation of cpu_stop, the * above condition is already met when the control reaches * this point and the following smp_mb() is not strictly * necessary. Do smp_mb() anyway for documentation and * robustness against future implementation changes. */ smp_mb(); /* See above comment block. */ return 0; } /** * synchronize_sched_expedited - Brute-force RCU-sched grace period * * Wait for an RCU-sched grace period to elapse, but use a "big hammer" * approach to force the grace period to end quickly. This consumes * significant time on all CPUs and is unfriendly to real-time workloads, * so is thus not recommended for any sort of common-case code. In fact, * if you are using synchronize_sched_expedited() in a loop, please * restructure your code to batch your updates, and then use a single * synchronize_sched() instead. * * This implementation can be thought of as an application of ticket * locking to RCU, with sync_sched_expedited_started and * sync_sched_expedited_done taking on the roles of the halves * of the ticket-lock word. Each task atomically increments * sync_sched_expedited_started upon entry, snapshotting the old value, * then attempts to stop all the CPUs. If this succeeds, then each * CPU will have executed a context switch, resulting in an RCU-sched * grace period. We are then done, so we use atomic_cmpxchg() to * update sync_sched_expedited_done to match our snapshot -- but * only if someone else has not already advanced past our snapshot. * * On the other hand, if try_stop_cpus() fails, we check the value * of sync_sched_expedited_done. If it has advanced past our * initial snapshot, then someone else must have forced a grace period * some time after we took our snapshot. In this case, our work is * done for us, and we can simply return. Otherwise, we try again, * but keep our initial snapshot for purposes of checking for someone * doing our work for us. * * If we fail too many times in a row, we fall back to synchronize_sched(). */ void synchronize_sched_expedited(void) { cpumask_var_t cm; bool cma = false; int cpu; long firstsnap, s, snap; int trycount = 0; struct rcu_state *rsp = &rcu_sched_state; /* * If we are in danger of counter wrap, just do synchronize_sched(). * By allowing sync_sched_expedited_started to advance no more than * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring * that more than 3.5 billion CPUs would be required to force a * counter wrap on a 32-bit system. Quite a few more CPUs would of * course be required on a 64-bit system. */ if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start), (ulong)atomic_long_read(&rsp->expedited_done) + ULONG_MAX / 8)) { wait_rcu_gp(call_rcu_sched); atomic_long_inc(&rsp->expedited_wrap); return; } /* * Take a ticket. Note that atomic_inc_return() implies a * full memory barrier. */ snap = atomic_long_inc_return(&rsp->expedited_start); firstsnap = snap; if (!try_get_online_cpus()) { /* CPU hotplug operation in flight, fall back to normal GP. */ wait_rcu_gp(call_rcu_sched); atomic_long_inc(&rsp->expedited_normal); return; } WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id())); /* Offline CPUs, idle CPUs, and any CPU we run on are quiescent. */ cma = zalloc_cpumask_var(&cm, GFP_KERNEL); if (cma) { cpumask_copy(cm, cpu_online_mask); cpumask_clear_cpu(raw_smp_processor_id(), cm); for_each_cpu(cpu, cm) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); if (!(atomic_add_return(0, &rdtp->dynticks) & 0x1)) cpumask_clear_cpu(cpu, cm); } if (cpumask_weight(cm) == 0) goto all_cpus_idle; } /* * Each pass through the following loop attempts to force a * context switch on each CPU. */ while (try_stop_cpus(cma ? cm : cpu_online_mask, synchronize_sched_expedited_cpu_stop, NULL) == -EAGAIN) { put_online_cpus(); atomic_long_inc(&rsp->expedited_tryfail); /* Check to see if someone else did our work for us. */ s = atomic_long_read(&rsp->expedited_done); if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) { /* ensure test happens before caller kfree */ smp_mb__before_atomic(); /* ^^^ */ atomic_long_inc(&rsp->expedited_workdone1); free_cpumask_var(cm); return; } /* No joy, try again later. Or just synchronize_sched(). */ if (trycount++ < 10) { udelay(trycount * num_online_cpus()); } else { wait_rcu_gp(call_rcu_sched); atomic_long_inc(&rsp->expedited_normal); free_cpumask_var(cm); return; } /* Recheck to see if someone else did our work for us. */ s = atomic_long_read(&rsp->expedited_done); if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) { /* ensure test happens before caller kfree */ smp_mb__before_atomic(); /* ^^^ */ atomic_long_inc(&rsp->expedited_workdone2); free_cpumask_var(cm); return; } /* * Refetching sync_sched_expedited_started allows later * callers to piggyback on our grace period. We retry * after they started, so our grace period works for them, * and they started after our first try, so their grace * period works for us. */ if (!try_get_online_cpus()) { /* CPU hotplug operation in flight, use normal GP. */ wait_rcu_gp(call_rcu_sched); atomic_long_inc(&rsp->expedited_normal); free_cpumask_var(cm); return; } snap = atomic_long_read(&rsp->expedited_start); smp_mb(); /* ensure read is before try_stop_cpus(). */ } atomic_long_inc(&rsp->expedited_stoppedcpus); all_cpus_idle: free_cpumask_var(cm); /* * Everyone up to our most recent fetch is covered by our grace * period. Update the counter, but only if our work is still * relevant -- which it won't be if someone who started later * than we did already did their update. */ do { atomic_long_inc(&rsp->expedited_done_tries); s = atomic_long_read(&rsp->expedited_done); if (ULONG_CMP_GE((ulong)s, (ulong)snap)) { /* ensure test happens before caller kfree */ smp_mb__before_atomic(); /* ^^^ */ atomic_long_inc(&rsp->expedited_done_lost); break; } } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s); atomic_long_inc(&rsp->expedited_done_exit); put_online_cpus(); } EXPORT_SYMBOL_GPL(synchronize_sched_expedited); /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, for the specified type of RCU, returning 1 if so. * The checks are in order of increasing expense: checks that can be * carried out against CPU-local state are performed first. However, * we must check for CPU stalls first, else we might not get a chance. */ static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp) { struct rcu_node *rnp = rdp->mynode; rdp->n_rcu_pending++; /* Check for CPU stalls, if enabled. */ check_cpu_stall(rsp, rdp); /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */ if (rcu_nohz_full_cpu(rsp)) return 0; /* Is the RCU core waiting for a quiescent state from this CPU? */ if (rcu_scheduler_fully_active && rdp->qs_pending && !rdp->passed_quiesce && rdp->rcu_qs_ctr_snap == __this_cpu_read(rcu_qs_ctr)) { rdp->n_rp_qs_pending++; } else if (rdp->qs_pending && (rdp->passed_quiesce || rdp->rcu_qs_ctr_snap != __this_cpu_read(rcu_qs_ctr))) { rdp->n_rp_report_qs++; return 1; } /* Does this CPU have callbacks ready to invoke? */ if (cpu_has_callbacks_ready_to_invoke(rdp)) { rdp->n_rp_cb_ready++; return 1; } /* Has RCU gone idle with this CPU needing another grace period? */ if (cpu_needs_another_gp(rsp, rdp)) { rdp->n_rp_cpu_needs_gp++; return 1; } /* Has another RCU grace period completed? */ if (READ_ONCE(rnp->completed) != rdp->completed) { /* outside lock */ rdp->n_rp_gp_completed++; return 1; } /* Has a new RCU grace period started? */ if (READ_ONCE(rnp->gpnum) != rdp->gpnum || unlikely(READ_ONCE(rdp->gpwrap))) { /* outside lock */ rdp->n_rp_gp_started++; return 1; } /* Does this CPU need a deferred NOCB wakeup? */ if (rcu_nocb_need_deferred_wakeup(rdp)) { rdp->n_rp_nocb_defer_wakeup++; return 1; } /* nothing to do */ rdp->n_rp_need_nothing++; return 0; } /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ static int rcu_pending(void) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda))) return 1; return 0; } /* * Return true if the specified CPU has any callback. If all_lazy is * non-NULL, store an indication of whether all callbacks are lazy. * (If there are no callbacks, all of them are deemed to be lazy.) */ static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy) { bool al = true; bool hc = false; struct rcu_data *rdp; struct rcu_state *rsp; for_each_rcu_flavor(rsp) { rdp = this_cpu_ptr(rsp->rda); if (!rdp->nxtlist) continue; hc = true; if (rdp->qlen != rdp->qlen_lazy || !all_lazy) { al = false; break; } } if (all_lazy) *all_lazy = al; return hc; } /* * Helper function for _rcu_barrier() tracing. If tracing is disabled, * the compiler is expected to optimize this away. */ static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s, int cpu, unsigned long done) { trace_rcu_barrier(rsp->name, s, cpu, atomic_read(&rsp->barrier_cpu_count), done); } /* * RCU callback function for _rcu_barrier(). If we are last, wake * up the task executing _rcu_barrier(). */ static void rcu_barrier_callback(struct rcu_head *rhp) { struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head); struct rcu_state *rsp = rdp->rsp; if (atomic_dec_and_test(&rsp->barrier_cpu_count)) { _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done); complete(&rsp->barrier_completion); } else { _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done); } } /* * Called with preemption disabled, and from cross-cpu IRQ context. */ static void rcu_barrier_func(void *type) { struct rcu_state *rsp = type; struct rcu_data *rdp = raw_cpu_ptr(rsp->rda); _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done); atomic_inc(&rsp->barrier_cpu_count); rsp->call(&rdp->barrier_head, rcu_barrier_callback); } /* * Orchestrate the specified type of RCU barrier, waiting for all * RCU callbacks of the specified type to complete. */ static void _rcu_barrier(struct rcu_state *rsp) { int cpu; struct rcu_data *rdp; unsigned long snap = READ_ONCE(rsp->n_barrier_done); unsigned long snap_done; _rcu_barrier_trace(rsp, "Begin", -1, snap); /* Take mutex to serialize concurrent rcu_barrier() requests. */ mutex_lock(&rsp->barrier_mutex); /* * Ensure that all prior references, including to ->n_barrier_done, * are ordered before the _rcu_barrier() machinery. */ smp_mb(); /* See above block comment. */ /* * Recheck ->n_barrier_done to see if others did our work for us. * This means checking ->n_barrier_done for an even-to-odd-to-even * transition. The "if" expression below therefore rounds the old * value up to the next even number and adds two before comparing. */ snap_done = rsp->n_barrier_done; _rcu_barrier_trace(rsp, "Check", -1, snap_done); /* * If the value in snap is odd, we needed to wait for the current * rcu_barrier() to complete, then wait for the next one, in other * words, we need the value of snap_done to be three larger than * the value of snap. On the other hand, if the value in snap is * even, we only had to wait for the next rcu_barrier() to complete, * in other words, we need the value of snap_done to be only two * greater than the value of snap. The "(snap + 3) & ~0x1" computes * this for us (thank you, Linus!). */ if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) { _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rsp->barrier_mutex); return; } /* * Increment ->n_barrier_done to avoid duplicate work. Use * WRITE_ONCE() to prevent the compiler from speculating * the increment to precede the early-exit check. */ WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1); WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1); _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done); smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */ /* * Initialize the count to one rather than to zero in order to * avoid a too-soon return to zero in case of a short grace period * (or preemption of this task). Exclude CPU-hotplug operations * to ensure that no offline CPU has callbacks queued. */ init_completion(&rsp->barrier_completion); atomic_set(&rsp->barrier_cpu_count, 1); get_online_cpus(); /* * Force each CPU with callbacks to register a new callback. * When that callback is invoked, we will know that all of the * corresponding CPU's preceding callbacks have been invoked. */ for_each_possible_cpu(cpu) { if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu)) continue; rdp = per_cpu_ptr(rsp->rda, cpu); if (rcu_is_nocb_cpu(cpu)) { if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) { _rcu_barrier_trace(rsp, "OfflineNoCB", cpu, rsp->n_barrier_done); } else { _rcu_barrier_trace(rsp, "OnlineNoCB", cpu, rsp->n_barrier_done); smp_mb__before_atomic(); atomic_inc(&rsp->barrier_cpu_count); __call_rcu(&rdp->barrier_head, rcu_barrier_callback, rsp, cpu, 0); } } else if (READ_ONCE(rdp->qlen)) { _rcu_barrier_trace(rsp, "OnlineQ", cpu, rsp->n_barrier_done); smp_call_function_single(cpu, rcu_barrier_func, rsp, 1); } else { _rcu_barrier_trace(rsp, "OnlineNQ", cpu, rsp->n_barrier_done); } } put_online_cpus(); /* * Now that we have an rcu_barrier_callback() callback on each * CPU, and thus each counted, remove the initial count. */ if (atomic_dec_and_test(&rsp->barrier_cpu_count)) complete(&rsp->barrier_completion); /* Increment ->n_barrier_done to prevent duplicate work. */ smp_mb(); /* Keep increment after above mechanism. */ WRITE_ONCE(rsp->n_barrier_done, rsp->n_barrier_done + 1); WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0); _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done); smp_mb(); /* Keep increment before caller's subsequent code. */ /* Wait for all rcu_barrier_callback() callbacks to be invoked. */ wait_for_completion(&rsp->barrier_completion); /* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rsp->barrier_mutex); } /** * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete. */ void rcu_barrier_bh(void) { _rcu_barrier(&rcu_bh_state); } EXPORT_SYMBOL_GPL(rcu_barrier_bh); /** * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks. */ void rcu_barrier_sched(void) { _rcu_barrier(&rcu_sched_state); } EXPORT_SYMBOL_GPL(rcu_barrier_sched); /* * Propagate ->qsinitmask bits up the rcu_node tree to account for the * first CPU in a given leaf rcu_node structure coming online. The caller * must hold the corresponding leaf rcu_node ->lock with interrrupts * disabled. */ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf) { long mask; struct rcu_node *rnp = rnp_leaf; for (;;) { mask = rnp->grpmask; rnp = rnp->parent; if (rnp == NULL) return; raw_spin_lock(&rnp->lock); /* Interrupts already disabled. */ rnp->qsmaskinit |= mask; raw_spin_unlock(&rnp->lock); /* Interrupts remain disabled. */ } } /* * Do boot-time initialization of a CPU's per-CPU RCU data. */ static void __init rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) { unsigned long flags; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo); rdp->dynticks = &per_cpu(rcu_dynticks, cpu); WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE); WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1); rdp->cpu = cpu; rdp->rsp = rsp; rcu_boot_init_nocb_percpu_data(rdp); raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Initialize a CPU's per-CPU RCU data. Note that only one online or * offline event can be happening at a given time. Note also that we * can accept some slop in the rsp->completed access due to the fact * that this CPU cannot possibly have any RCU callbacks in flight yet. */ static void rcu_init_percpu_data(int cpu, struct rcu_state *rsp) { unsigned long flags; unsigned long mask; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_node *rnp = rcu_get_root(rsp); /* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave(&rnp->lock, flags); rdp->beenonline = 1; /* We have now been online. */ rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; if (!rdp->nxtlist) init_callback_list(rdp); /* Re-enable callbacks on this CPU. */ rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_sysidle_init_percpu_data(rdp->dynticks); atomic_set(&rdp->dynticks->dynticks, (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* * Add CPU to leaf rcu_node pending-online bitmask. Any needed * propagation up the rcu_node tree will happen at the beginning * of the next grace period. */ rnp = rdp->mynode; mask = rdp->grpmask; raw_spin_lock(&rnp->lock); /* irqs already disabled. */ smp_mb__after_unlock_lock(); rnp->qsmaskinitnext |= mask; rdp->gpnum = rnp->completed; /* Make CPU later note any new GP. */ rdp->completed = rnp->completed; rdp->passed_quiesce = false; rdp->rcu_qs_ctr_snap = per_cpu(rcu_qs_ctr, cpu); rdp->qs_pending = false; trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl")); raw_spin_unlock_irqrestore(&rnp->lock, flags); } static void rcu_prepare_cpu(int cpu) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) rcu_init_percpu_data(cpu, rsp); } /* * Handle CPU online/offline notification events. */ int rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { long cpu = (long)hcpu; struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu); struct rcu_node *rnp = rdp->mynode; struct rcu_state *rsp; switch (action) { case CPU_UP_PREPARE: case CPU_UP_PREPARE_FROZEN: rcu_prepare_cpu(cpu); rcu_prepare_kthreads(cpu); rcu_spawn_all_nocb_kthreads(cpu); break; case CPU_ONLINE: case CPU_DOWN_FAILED: rcu_boost_kthread_setaffinity(rnp, -1); break; case CPU_DOWN_PREPARE: rcu_boost_kthread_setaffinity(rnp, cpu); break; case CPU_DYING: case CPU_DYING_FROZEN: for_each_rcu_flavor(rsp) rcu_cleanup_dying_cpu(rsp); break; case CPU_DYING_IDLE: for_each_rcu_flavor(rsp) { rcu_cleanup_dying_idle_cpu(cpu, rsp); } break; case CPU_DEAD: case CPU_DEAD_FROZEN: case CPU_UP_CANCELED: case CPU_UP_CANCELED_FROZEN: for_each_rcu_flavor(rsp) { rcu_cleanup_dead_cpu(cpu, rsp); do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu)); } break; default: break; } return NOTIFY_OK; } static int rcu_pm_notify(struct notifier_block *self, unsigned long action, void *hcpu) { switch (action) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ rcu_expedite_gp(); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */ rcu_unexpedite_gp(); break; default: break; } return NOTIFY_OK; } /* * Spawn the kthreads that handle each RCU flavor's grace periods. */ static int __init rcu_spawn_gp_kthread(void) { unsigned long flags; int kthread_prio_in = kthread_prio; struct rcu_node *rnp; struct rcu_state *rsp; struct sched_param sp; struct task_struct *t; /* Force priority into range. */ if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1) kthread_prio = 1; else if (kthread_prio < 0) kthread_prio = 0; else if (kthread_prio > 99) kthread_prio = 99; if (kthread_prio != kthread_prio_in) pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n", kthread_prio, kthread_prio_in); rcu_scheduler_fully_active = 1; for_each_rcu_flavor(rsp) { t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name); BUG_ON(IS_ERR(t)); rnp = rcu_get_root(rsp); raw_spin_lock_irqsave(&rnp->lock, flags); rsp->gp_kthread = t; if (kthread_prio) { sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); } wake_up_process(t); raw_spin_unlock_irqrestore(&rnp->lock, flags); } rcu_spawn_nocb_kthreads(); rcu_spawn_boost_kthreads(); return 0; } early_initcall(rcu_spawn_gp_kthread); /* * This function is invoked towards the end of the scheduler's initialization * process. Before this is called, the idle task might contain * RCU read-side critical sections (during which time, this idle * task is booting the system). After this function is called, the * idle tasks are prohibited from containing RCU read-side critical * sections. This function also enables RCU lockdep checking. */ void rcu_scheduler_starting(void) { WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_scheduler_active = 1; } /* * Compute the per-level fanout, either using the exact fanout specified * or balancing the tree, depending on the rcu_fanout_exact boot parameter. */ static void __init rcu_init_levelspread(struct rcu_state *rsp) { int i; if (rcu_fanout_exact) { rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf; for (i = rcu_num_lvls - 2; i >= 0; i--) rsp->levelspread[i] = RCU_FANOUT; } else { int ccur; int cprv; cprv = nr_cpu_ids; for (i = rcu_num_lvls - 1; i >= 0; i--) { ccur = rsp->levelcnt[i]; rsp->levelspread[i] = (cprv + ccur - 1) / ccur; cprv = ccur; } } } /* * Helper function for rcu_init() that initializes one rcu_state structure. */ static void __init rcu_init_one(struct rcu_state *rsp, struct rcu_data __percpu *rda) { static const char * const buf[] = { "rcu_node_0", "rcu_node_1", "rcu_node_2", "rcu_node_3" }; /* Match MAX_RCU_LVLS */ static const char * const fqs[] = { "rcu_node_fqs_0", "rcu_node_fqs_1", "rcu_node_fqs_2", "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */ static u8 fl_mask = 0x1; int cpustride = 1; int i; int j; struct rcu_node *rnp; BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */ /* Silence gcc 4.8 false positive about array index out of range. */ if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS) panic("rcu_init_one: rcu_num_lvls out of range"); /* Initialize the level-tracking arrays. */ for (i = 0; i < rcu_num_lvls; i++) rsp->levelcnt[i] = num_rcu_lvl[i]; for (i = 1; i < rcu_num_lvls; i++) rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1]; rcu_init_levelspread(rsp); rsp->flavor_mask = fl_mask; fl_mask <<= 1; /* Initialize the elements themselves, starting from the leaves. */ for (i = rcu_num_lvls - 1; i >= 0; i--) { cpustride *= rsp->levelspread[i]; rnp = rsp->level[i]; for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) { raw_spin_lock_init(&rnp->lock); lockdep_set_class_and_name(&rnp->lock, &rcu_node_class[i], buf[i]); raw_spin_lock_init(&rnp->fqslock); lockdep_set_class_and_name(&rnp->fqslock, &rcu_fqs_class[i], fqs[i]); rnp->gpnum = rsp->gpnum; rnp->completed = rsp->completed; rnp->qsmask = 0; rnp->qsmaskinit = 0; rnp->grplo = j * cpustride; rnp->grphi = (j + 1) * cpustride - 1; if (rnp->grphi >= nr_cpu_ids) rnp->grphi = nr_cpu_ids - 1; if (i == 0) { rnp->grpnum = 0; rnp->grpmask = 0; rnp->parent = NULL; } else { rnp->grpnum = j % rsp->levelspread[i - 1]; rnp->grpmask = 1UL << rnp->grpnum; rnp->parent = rsp->level[i - 1] + j / rsp->levelspread[i - 1]; } rnp->level = i; INIT_LIST_HEAD(&rnp->blkd_tasks); rcu_init_one_nocb(rnp); } } init_waitqueue_head(&rsp->gp_wq); rnp = rsp->level[rcu_num_lvls - 1]; for_each_possible_cpu(i) { while (i > rnp->grphi) rnp++; per_cpu_ptr(rsp->rda, i)->mynode = rnp; rcu_boot_init_percpu_data(i, rsp); } list_add(&rsp->flavors, &rcu_struct_flavors); } /* * Compute the rcu_node tree geometry from kernel parameters. This cannot * replace the definitions in tree.h because those are needed to size * the ->node array in the rcu_state structure. */ static void __init rcu_init_geometry(void) { ulong d; int i; int j; int n = nr_cpu_ids; int rcu_capacity[MAX_RCU_LVLS + 1]; /* * Initialize any unspecified boot parameters. * The default values of jiffies_till_first_fqs and * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS * value, which is a function of HZ, then adding one for each * RCU_JIFFIES_FQS_DIV CPUs that might be on the system. */ d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; if (jiffies_till_first_fqs == ULONG_MAX) jiffies_till_first_fqs = d; if (jiffies_till_next_fqs == ULONG_MAX) jiffies_till_next_fqs = d; /* If the compile-time values are accurate, just leave. */ if (rcu_fanout_leaf == RCU_FANOUT_LEAF && nr_cpu_ids == NR_CPUS) return; pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n", rcu_fanout_leaf, nr_cpu_ids); /* * Compute number of nodes that can be handled an rcu_node tree * with the given number of levels. Setting rcu_capacity[0] makes * some of the arithmetic easier. */ rcu_capacity[0] = 1; rcu_capacity[1] = rcu_fanout_leaf; for (i = 2; i <= MAX_RCU_LVLS; i++) rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT; /* * The boot-time rcu_fanout_leaf parameter is only permitted * to increase the leaf-level fanout, not decrease it. Of course, * the leaf-level fanout cannot exceed the number of bits in * the rcu_node masks. Finally, the tree must be able to accommodate * the configured number of CPUs. Complain and fall back to the * compile-time values if these limits are exceeded. */ if (rcu_fanout_leaf < RCU_FANOUT_LEAF || rcu_fanout_leaf > sizeof(unsigned long) * 8 || n > rcu_capacity[MAX_RCU_LVLS]) { WARN_ON(1); return; } /* Calculate the number of rcu_nodes at each level of the tree. */ for (i = 1; i <= MAX_RCU_LVLS; i++) if (n <= rcu_capacity[i]) { for (j = 0; j <= i; j++) num_rcu_lvl[j] = DIV_ROUND_UP(n, rcu_capacity[i - j]); rcu_num_lvls = i; for (j = i + 1; j <= MAX_RCU_LVLS; j++) num_rcu_lvl[j] = 0; break; } /* Calculate the total number of rcu_node structures. */ rcu_num_nodes = 0; for (i = 0; i <= MAX_RCU_LVLS; i++) rcu_num_nodes += num_rcu_lvl[i]; rcu_num_nodes -= n; } /* * Dump out the structure of the rcu_node combining tree associated * with the rcu_state structure referenced by rsp. */ static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp) { int level = 0; struct rcu_node *rnp; pr_info("rcu_node tree layout dump\n"); pr_info(" "); rcu_for_each_node_breadth_first(rsp, rnp) { if (rnp->level != level) { pr_cont("\n"); pr_info(" "); level = rnp->level; } pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum); } pr_cont("\n"); } void __init rcu_init(void) { int cpu; rcu_early_boot_tests(); rcu_bootup_announce(); rcu_init_geometry(); rcu_init_one(&rcu_bh_state, &rcu_bh_data); rcu_init_one(&rcu_sched_state, &rcu_sched_data); if (dump_tree) rcu_dump_rcu_node_tree(&rcu_sched_state); __rcu_init_preempt(); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); /* * We don't need protection against CPU-hotplug here because * this is called early in boot, before either interrupts * or the scheduler are operational. */ cpu_notifier(rcu_cpu_notify, 0); pm_notifier(rcu_pm_notify, 0); for_each_online_cpu(cpu) rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu); } #include "tree_plugin.h"