/* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * Internal non-public definitions that provide either classic * or preemptible semantics. * * 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, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * Copyright Red Hat, 2009 * Copyright IBM Corporation, 2009 * * Author: Ingo Molnar <mingo@elte.hu> * Paul E. McKenney <paulmck@linux.vnet.ibm.com> */ #include <linux/delay.h> #include <linux/oom.h> #include <linux/smpboot.h> #define RCU_KTHREAD_PRIO 1 #ifdef CONFIG_RCU_BOOST #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO #else #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO #endif /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary. If you like #ifdef, you * will love this function. */ static void __init rcu_bootup_announce_oddness(void) { #ifdef CONFIG_RCU_TRACE printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n"); #endif #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32) printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n", CONFIG_RCU_FANOUT); #endif #ifdef CONFIG_RCU_FANOUT_EXACT printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n"); #endif #ifdef CONFIG_RCU_FAST_NO_HZ printk(KERN_INFO "\tRCU dyntick-idle grace-period acceleration is enabled.\n"); #endif #ifdef CONFIG_PROVE_RCU printk(KERN_INFO "\tRCU lockdep checking is enabled.\n"); #endif #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE printk(KERN_INFO "\tRCU torture testing starts during boot.\n"); #endif #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE) printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n"); #endif #if defined(CONFIG_RCU_CPU_STALL_INFO) printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n"); #endif #if NUM_RCU_LVL_4 != 0 printk(KERN_INFO "\tFour-level hierarchy is enabled.\n"); #endif if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF) printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf); if (nr_cpu_ids != NR_CPUS) printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids); } #ifdef CONFIG_TREE_PREEMPT_RCU struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt, call_rcu); DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data); static struct rcu_state *rcu_state = &rcu_preempt_state; static int rcu_preempted_readers_exp(struct rcu_node *rnp); /* * Tell them what RCU they are running. */ static void __init rcu_bootup_announce(void) { printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n"); rcu_bootup_announce_oddness(); } /* * Return the number of RCU-preempt batches processed thus far * for debug and statistics. */ long rcu_batches_completed_preempt(void) { return rcu_preempt_state.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt); /* * Return the number of RCU batches processed thus far for debug & stats. */ long rcu_batches_completed(void) { return rcu_batches_completed_preempt(); } EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Force a quiescent state for preemptible RCU. */ void rcu_force_quiescent_state(void) { force_quiescent_state(&rcu_preempt_state); } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); /* * Record a preemptible-RCU quiescent state for the specified CPU. Note * that this just means that the task currently running on the CPU is * not in a quiescent state. There might be any number of tasks blocked * while in an RCU read-side critical section. * * Unlike the other rcu_*_qs() functions, callers to this function * must disable irqs in order to protect the assignment to * ->rcu_read_unlock_special. */ static void rcu_preempt_qs(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); if (rdp->passed_quiesce == 0) trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs"); rdp->passed_quiesce = 1; current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS; } /* * We have entered the scheduler, and the current task might soon be * context-switched away from. If this task is in an RCU read-side * critical section, we will no longer be able to rely on the CPU to * record that fact, so we enqueue the task on the blkd_tasks list. * The task will dequeue itself when it exits the outermost enclosing * RCU read-side critical section. Therefore, the current grace period * cannot be permitted to complete until the blkd_tasks list entries * predating the current grace period drain, in other words, until * rnp->gp_tasks becomes NULL. * * Caller must disable preemption. */ static void rcu_preempt_note_context_switch(int cpu) { struct task_struct *t = current; unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp; if (t->rcu_read_lock_nesting > 0 && (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) { /* Possibly blocking in an RCU read-side critical section. */ rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu); rnp = rdp->mynode; raw_spin_lock_irqsave(&rnp->lock, flags); t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED; t->rcu_blocked_node = rnp; /* * If this CPU has already checked in, then this task * will hold up the next grace period rather than the * current grace period. Queue the task accordingly. * If the task is queued for the current grace period * (i.e., this CPU has not yet passed through a quiescent * state for the current grace period), then as long * as that task remains queued, the current grace period * cannot end. Note that there is some uncertainty as * to exactly when the current grace period started. * We take a conservative approach, which can result * in unnecessarily waiting on tasks that started very * slightly after the current grace period began. C'est * la vie!!! * * But first, note that the current CPU must still be * on line! */ WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0); WARN_ON_ONCE(!list_empty(&t->rcu_node_entry)); if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) { list_add(&t->rcu_node_entry, rnp->gp_tasks->prev); rnp->gp_tasks = &t->rcu_node_entry; #ifdef CONFIG_RCU_BOOST if (rnp->boost_tasks != NULL) rnp->boost_tasks = rnp->gp_tasks; #endif /* #ifdef CONFIG_RCU_BOOST */ } else { list_add(&t->rcu_node_entry, &rnp->blkd_tasks); if (rnp->qsmask & rdp->grpmask) rnp->gp_tasks = &t->rcu_node_entry; } trace_rcu_preempt_task(rdp->rsp->name, t->pid, (rnp->qsmask & rdp->grpmask) ? rnp->gpnum : rnp->gpnum + 1); raw_spin_unlock_irqrestore(&rnp->lock, flags); } else if (t->rcu_read_lock_nesting < 0 && t->rcu_read_unlock_special) { /* * Complete exit from RCU read-side critical section on * behalf of preempted instance of __rcu_read_unlock(). */ rcu_read_unlock_special(t); } /* * Either we were not in an RCU read-side critical section to * begin with, or we have now recorded that critical section * globally. Either way, we can now note a quiescent state * for this CPU. Again, if we were in an RCU read-side critical * section, and if that critical section was blocking the current * grace period, then the fact that the task has been enqueued * means that we continue to block the current grace period. */ local_irq_save(flags); rcu_preempt_qs(cpu); local_irq_restore(flags); } /* * Check for preempted RCU readers blocking the current grace period * for the specified rcu_node structure. If the caller needs a reliable * answer, it must hold the rcu_node's ->lock. */ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) { return rnp->gp_tasks != NULL; } /* * 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_node *rnp, unsigned long flags) __releases(rnp->lock) { unsigned long mask; struct rcu_node *rnp_p; if (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) { /* * Either there is only one rcu_node in the tree, * or tasks were kicked up to root rcu_node due to * CPUs going offline. */ rcu_report_qs_rsp(&rcu_preempt_state, flags); return; } /* Report up the rest of the hierarchy. */ mask = rnp->grpmask; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */ rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags); } /* * Advance a ->blkd_tasks-list pointer to the next entry, instead * returning NULL if at the end of the list. */ static struct list_head *rcu_next_node_entry(struct task_struct *t, struct rcu_node *rnp) { struct list_head *np; np = t->rcu_node_entry.next; if (np == &rnp->blkd_tasks) np = NULL; return np; } /* * Handle special cases during rcu_read_unlock(), such as needing to * notify RCU core processing or task having blocked during the RCU * read-side critical section. */ void rcu_read_unlock_special(struct task_struct *t) { int empty; int empty_exp; int empty_exp_now; unsigned long flags; struct list_head *np; #ifdef CONFIG_RCU_BOOST struct rt_mutex *rbmp = NULL; #endif /* #ifdef CONFIG_RCU_BOOST */ struct rcu_node *rnp; int special; /* NMI handlers cannot block and cannot safely manipulate state. */ if (in_nmi()) return; local_irq_save(flags); /* * If RCU core is waiting for this CPU to exit critical section, * let it know that we have done so. */ special = t->rcu_read_unlock_special; if (special & RCU_READ_UNLOCK_NEED_QS) { rcu_preempt_qs(smp_processor_id()); } /* Hardware IRQ handlers cannot block. */ if (in_irq() || in_serving_softirq()) { local_irq_restore(flags); return; } /* Clean up if blocked during RCU read-side critical section. */ if (special & RCU_READ_UNLOCK_BLOCKED) { t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED; /* * Remove this task from the list it blocked on. The * task can migrate while we acquire the lock, but at * most one time. So at most two passes through loop. */ for (;;) { rnp = t->rcu_blocked_node; raw_spin_lock(&rnp->lock); /* irqs already disabled. */ if (rnp == t->rcu_blocked_node) break; raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ } empty = !rcu_preempt_blocked_readers_cgp(rnp); empty_exp = !rcu_preempted_readers_exp(rnp); smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */ np = rcu_next_node_entry(t, rnp); list_del_init(&t->rcu_node_entry); t->rcu_blocked_node = NULL; trace_rcu_unlock_preempted_task("rcu_preempt", rnp->gpnum, t->pid); if (&t->rcu_node_entry == rnp->gp_tasks) rnp->gp_tasks = np; if (&t->rcu_node_entry == rnp->exp_tasks) rnp->exp_tasks = np; #ifdef CONFIG_RCU_BOOST if (&t->rcu_node_entry == rnp->boost_tasks) rnp->boost_tasks = np; /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */ if (t->rcu_boost_mutex) { rbmp = t->rcu_boost_mutex; t->rcu_boost_mutex = NULL; } #endif /* #ifdef CONFIG_RCU_BOOST */ /* * If this was the last task on the current list, and if * we aren't waiting on any CPUs, report the quiescent state. * Note that rcu_report_unblock_qs_rnp() releases rnp->lock, * so we must take a snapshot of the expedited state. */ empty_exp_now = !rcu_preempted_readers_exp(rnp); if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) { trace_rcu_quiescent_state_report("preempt_rcu", rnp->gpnum, 0, rnp->qsmask, rnp->level, rnp->grplo, rnp->grphi, !!rnp->gp_tasks); rcu_report_unblock_qs_rnp(rnp, flags); } else { raw_spin_unlock_irqrestore(&rnp->lock, flags); } #ifdef CONFIG_RCU_BOOST /* Unboost if we were boosted. */ if (rbmp) rt_mutex_unlock(rbmp); #endif /* #ifdef CONFIG_RCU_BOOST */ /* * If this was the last task on the expedited lists, * then we need to report up the rcu_node hierarchy. */ if (!empty_exp && empty_exp_now) rcu_report_exp_rnp(&rcu_preempt_state, rnp, true); } else { local_irq_restore(flags); } } #ifdef CONFIG_RCU_CPU_STALL_VERBOSE /* * Dump detailed information for all tasks blocking the current RCU * grace period on the specified rcu_node structure. */ static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp) { unsigned long flags; struct task_struct *t; raw_spin_lock_irqsave(&rnp->lock, flags); if (!rcu_preempt_blocked_readers_cgp(rnp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } t = list_entry(rnp->gp_tasks, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) sched_show_task(t); raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* * Dump detailed information for all tasks blocking the current RCU * grace period. */ static void rcu_print_detail_task_stall(struct rcu_state *rsp) { struct rcu_node *rnp = rcu_get_root(rsp); rcu_print_detail_task_stall_rnp(rnp); rcu_for_each_leaf_node(rsp, rnp) rcu_print_detail_task_stall_rnp(rnp); } #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ static void rcu_print_detail_task_stall(struct rcu_state *rsp) { } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */ #ifdef CONFIG_RCU_CPU_STALL_INFO static void rcu_print_task_stall_begin(struct rcu_node *rnp) { printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):", rnp->level, rnp->grplo, rnp->grphi); } static void rcu_print_task_stall_end(void) { printk(KERN_CONT "\n"); } #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ static void rcu_print_task_stall_begin(struct rcu_node *rnp) { } static void rcu_print_task_stall_end(void) { } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */ /* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each. */ static int rcu_print_task_stall(struct rcu_node *rnp) { struct task_struct *t; int ndetected = 0; if (!rcu_preempt_blocked_readers_cgp(rnp)) return 0; rcu_print_task_stall_begin(rnp); t = list_entry(rnp->gp_tasks, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { printk(KERN_CONT " P%d", t->pid); ndetected++; } rcu_print_task_stall_end(); return ndetected; } /* * Check that the list of blocked tasks for the newly completed grace * period is in fact empty. It is a serious bug to complete a grace * period that still has RCU readers blocked! This function must be * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock * must be held by the caller. * * Also, if there are blocked tasks on the list, they automatically * block the newly created grace period, so set up ->gp_tasks accordingly. */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) { WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)); if (!list_empty(&rnp->blkd_tasks)) rnp->gp_tasks = rnp->blkd_tasks.next; WARN_ON_ONCE(rnp->qsmask); } #ifdef CONFIG_HOTPLUG_CPU /* * Handle tasklist migration for case in which all CPUs covered by the * specified rcu_node have gone offline. Move them up to the root * rcu_node. The reason for not just moving them to the immediate * parent is to remove the need for rcu_read_unlock_special() to * make more than two attempts to acquire the target rcu_node's lock. * Returns true if there were tasks blocking the current RCU grace * period. * * Returns 1 if there was previously a task blocking the current grace * period on the specified rcu_node structure. * * The caller must hold rnp->lock with irqs disabled. */ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { struct list_head *lp; struct list_head *lp_root; int retval = 0; struct rcu_node *rnp_root = rcu_get_root(rsp); struct task_struct *t; if (rnp == rnp_root) { WARN_ONCE(1, "Last CPU thought to be offlined?"); return 0; /* Shouldn't happen: at least one CPU online. */ } /* If we are on an internal node, complain bitterly. */ WARN_ON_ONCE(rnp != rdp->mynode); /* * Move tasks up to root rcu_node. Don't try to get fancy for * this corner-case operation -- just put this node's tasks * at the head of the root node's list, and update the root node's * ->gp_tasks and ->exp_tasks pointers to those of this node's, * if non-NULL. This might result in waiting for more tasks than * absolutely necessary, but this is a good performance/complexity * tradeoff. */ if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0) retval |= RCU_OFL_TASKS_NORM_GP; if (rcu_preempted_readers_exp(rnp)) retval |= RCU_OFL_TASKS_EXP_GP; lp = &rnp->blkd_tasks; lp_root = &rnp_root->blkd_tasks; while (!list_empty(lp)) { t = list_entry(lp->next, typeof(*t), rcu_node_entry); raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ list_del(&t->rcu_node_entry); t->rcu_blocked_node = rnp_root; list_add(&t->rcu_node_entry, lp_root); if (&t->rcu_node_entry == rnp->gp_tasks) rnp_root->gp_tasks = rnp->gp_tasks; if (&t->rcu_node_entry == rnp->exp_tasks) rnp_root->exp_tasks = rnp->exp_tasks; #ifdef CONFIG_RCU_BOOST if (&t->rcu_node_entry == rnp->boost_tasks) rnp_root->boost_tasks = rnp->boost_tasks; #endif /* #ifdef CONFIG_RCU_BOOST */ raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ } rnp->gp_tasks = NULL; rnp->exp_tasks = NULL; #ifdef CONFIG_RCU_BOOST rnp->boost_tasks = NULL; /* * In case root is being boosted and leaf was not. Make sure * that we boost the tasks blocking the current grace period * in this case. */ raw_spin_lock(&rnp_root->lock); /* irqs already disabled */ if (rnp_root->boost_tasks != NULL && rnp_root->boost_tasks != rnp_root->gp_tasks && rnp_root->boost_tasks != rnp_root->exp_tasks) rnp_root->boost_tasks = rnp_root->gp_tasks; raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */ #endif /* #ifdef CONFIG_RCU_BOOST */ return retval; } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * Check for a quiescent state from the current CPU. When a task blocks, * the task is recorded in the corresponding CPU's rcu_node structure, * which is checked elsewhere. * * Caller must disable hard irqs. */ static void rcu_preempt_check_callbacks(int cpu) { struct task_struct *t = current; if (t->rcu_read_lock_nesting == 0) { rcu_preempt_qs(cpu); return; } if (t->rcu_read_lock_nesting > 0 && per_cpu(rcu_preempt_data, cpu).qs_pending) t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS; } #ifdef CONFIG_RCU_BOOST static void rcu_preempt_do_callbacks(void) { rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data)); } #endif /* #ifdef CONFIG_RCU_BOOST */ /* * Queue a preemptible-RCU callback for invocation after a grace period. */ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_preempt_state, 0); } EXPORT_SYMBOL_GPL(call_rcu); /* * 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_preempt_state, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu); /** * synchronize_rcu - wait until a grace period has elapsed. * * Control will return to the caller some time after a full grace * period has elapsed, in other words after all currently executing RCU * read-side critical sections have completed. Note, however, that * upon return from synchronize_rcu(), the caller might well be executing * concurrently with new RCU read-side critical sections that began while * synchronize_rcu() was waiting. RCU read-side critical sections are * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested. */ void synchronize_rcu(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() in RCU read-side critical section"); if (!rcu_scheduler_active) return; wait_rcu_gp(call_rcu); } EXPORT_SYMBOL_GPL(synchronize_rcu); static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq); static unsigned long sync_rcu_preempt_exp_count; static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex); /* * Return non-zero if there are any tasks in RCU read-side critical * sections blocking the current preemptible-RCU expedited grace period. * If there is no preemptible-RCU expedited grace period currently in * progress, returns zero unconditionally. */ static int rcu_preempted_readers_exp(struct rcu_node *rnp) { return rnp->exp_tasks != NULL; } /* * return non-zero if there is no RCU expedited grace period in progress * for the specified rcu_node structure, in other words, if all CPUs and * tasks covered by the specified rcu_node structure have done their bit * for the current expedited grace period. Works only for preemptible * RCU -- other RCU implementation use other means. * * Caller must hold sync_rcu_preempt_exp_mutex. */ static int sync_rcu_preempt_exp_done(struct rcu_node *rnp) { return !rcu_preempted_readers_exp(rnp) && ACCESS_ONCE(rnp->expmask) == 0; } /* * Report the exit from RCU read-side critical section for the last task * that queued itself during or before the current expedited preemptible-RCU * grace period. This event is reported either to the rcu_node structure on * which the task was queued or to one of that rcu_node structure's ancestors, * recursively up the tree. (Calm down, calm down, we do the recursion * iteratively!) * * Most callers will set the "wake" flag, but the task initiating the * expedited grace period need not wake itself. * * Caller must hold sync_rcu_preempt_exp_mutex. */ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, bool wake) { unsigned long flags; unsigned long mask; raw_spin_lock_irqsave(&rnp->lock, flags); for (;;) { if (!sync_rcu_preempt_exp_done(rnp)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); break; } if (rnp->parent == NULL) { raw_spin_unlock_irqrestore(&rnp->lock, flags); if (wake) wake_up(&sync_rcu_preempt_exp_wq); break; } mask = rnp->grpmask; raw_spin_unlock(&rnp->lock); /* irqs remain disabled */ rnp = rnp->parent; raw_spin_lock(&rnp->lock); /* irqs already disabled */ rnp->expmask &= ~mask; } } /* * Snapshot the tasks blocking the newly started preemptible-RCU expedited * grace period for the specified rcu_node structure. If there are no such * tasks, report it up the rcu_node hierarchy. * * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock. */ static void sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp) { unsigned long flags; int must_wait = 0; raw_spin_lock_irqsave(&rnp->lock, flags); if (list_empty(&rnp->blkd_tasks)) { raw_spin_unlock_irqrestore(&rnp->lock, flags); } else { rnp->exp_tasks = rnp->blkd_tasks.next; rcu_initiate_boost(rnp, flags); /* releases rnp->lock */ must_wait = 1; } if (!must_wait) rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */ } /** * synchronize_rcu_expedited - Brute-force RCU grace period * * Wait for an RCU-preempt grace period, but expedite it. The basic * idea is to invoke synchronize_sched_expedited() to push all the tasks to * the ->blkd_tasks lists and wait for this list to drain. 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_rcu_expedited() in a loop, * please restructure your code to batch your updates, and then Use a * single synchronize_rcu() instead. * * Note that it is illegal to call this function while holding any lock * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal * to call this function from a CPU-hotplug notifier. Failing to observe * these restriction will result in deadlock. */ void synchronize_rcu_expedited(void) { unsigned long flags; struct rcu_node *rnp; struct rcu_state *rsp = &rcu_preempt_state; unsigned long snap; int trycount = 0; smp_mb(); /* Caller's modifications seen first by other CPUs. */ snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1; smp_mb(); /* Above access cannot bleed into critical section. */ /* * Block CPU-hotplug operations. This means that any CPU-hotplug * operation that finds an rcu_node structure with tasks in the * process of being boosted will know that all tasks blocking * this expedited grace period will already be in the process of * being boosted. This simplifies the process of moving tasks * from leaf to root rcu_node structures. */ get_online_cpus(); /* * Acquire lock, falling back to synchronize_rcu() if too many * lock-acquisition failures. Of course, if someone does the * expedited grace period for us, just leave. */ while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) { if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { put_online_cpus(); goto mb_ret; /* Others did our work for us. */ } if (trycount++ < 10) { udelay(trycount * num_online_cpus()); } else { put_online_cpus(); synchronize_rcu(); return; } } if (ULONG_CMP_LT(snap, ACCESS_ONCE(sync_rcu_preempt_exp_count))) { put_online_cpus(); goto unlock_mb_ret; /* Others did our work for us. */ } /* force all RCU readers onto ->blkd_tasks lists. */ synchronize_sched_expedited(); /* Initialize ->expmask for all non-leaf rcu_node structures. */ rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) { raw_spin_lock_irqsave(&rnp->lock, flags); rnp->expmask = rnp->qsmaskinit; raw_spin_unlock_irqrestore(&rnp->lock, flags); } /* Snapshot current state of ->blkd_tasks lists. */ rcu_for_each_leaf_node(rsp, rnp) sync_rcu_preempt_exp_init(rsp, rnp); if (NUM_RCU_NODES > 1) sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp)); put_online_cpus(); /* Wait for snapshotted ->blkd_tasks lists to drain. */ rnp = rcu_get_root(rsp); wait_event(sync_rcu_preempt_exp_wq, sync_rcu_preempt_exp_done(rnp)); /* Clean up and exit. */ smp_mb(); /* ensure expedited GP seen before counter increment. */ ACCESS_ONCE(sync_rcu_preempt_exp_count)++; unlock_mb_ret: mutex_unlock(&sync_rcu_preempt_exp_mutex); mb_ret: smp_mb(); /* ensure subsequent action seen after grace period. */ } EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); /** * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. */ void rcu_barrier(void) { _rcu_barrier(&rcu_preempt_state); } EXPORT_SYMBOL_GPL(rcu_barrier); /* * Initialize preemptible RCU's state structures. */ static void __init __rcu_init_preempt(void) { rcu_init_one(&rcu_preempt_state, &rcu_preempt_data); } #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ static struct rcu_state *rcu_state = &rcu_sched_state; /* * Tell them what RCU they are running. */ static void __init rcu_bootup_announce(void) { printk(KERN_INFO "Hierarchical RCU implementation.\n"); rcu_bootup_announce_oddness(); } /* * Return the number of RCU batches processed thus far for debug & stats. */ long rcu_batches_completed(void) { return rcu_batches_completed_sched(); } EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Force a quiescent state for RCU, which, because there is no preemptible * RCU, becomes the same as rcu-sched. */ void rcu_force_quiescent_state(void) { rcu_sched_force_quiescent_state(); } EXPORT_SYMBOL_GPL(rcu_force_quiescent_state); /* * Because preemptible RCU does not exist, we never have to check for * CPUs being in quiescent states. */ static void rcu_preempt_note_context_switch(int cpu) { } /* * Because preemptible RCU does not exist, there are never any preempted * RCU readers. */ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) { return 0; } #ifdef CONFIG_HOTPLUG_CPU /* Because preemptible RCU does not exist, no quieting of tasks. */ static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) { raw_spin_unlock_irqrestore(&rnp->lock, flags); } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * Because preemptible RCU does not exist, we never have to check for * tasks blocked within RCU read-side critical sections. */ static void rcu_print_detail_task_stall(struct rcu_state *rsp) { } /* * Because preemptible RCU does not exist, we never have to check for * tasks blocked within RCU read-side critical sections. */ static int rcu_print_task_stall(struct rcu_node *rnp) { return 0; } /* * Because there is no preemptible RCU, there can be no readers blocked, * so there is no need to check for blocked tasks. So check only for * bogus qsmask values. */ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) { WARN_ON_ONCE(rnp->qsmask); } #ifdef CONFIG_HOTPLUG_CPU /* * Because preemptible RCU does not exist, it never needs to migrate * tasks that were blocked within RCU read-side critical sections, and * such non-existent tasks cannot possibly have been blocking the current * grace period. */ static int rcu_preempt_offline_tasks(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp) { return 0; } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * Because preemptible RCU does not exist, it never has any callbacks * to check. */ static void rcu_preempt_check_callbacks(int cpu) { } /* * 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(). * * Because there is no preemptible RCU, we use RCU-sched instead. */ void kfree_call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_sched_state, 1); } EXPORT_SYMBOL_GPL(kfree_call_rcu); /* * Wait for an rcu-preempt grace period, but make it happen quickly. * But because preemptible RCU does not exist, map to rcu-sched. */ void synchronize_rcu_expedited(void) { synchronize_sched_expedited(); } EXPORT_SYMBOL_GPL(synchronize_rcu_expedited); #ifdef CONFIG_HOTPLUG_CPU /* * Because preemptible RCU does not exist, there is never any need to * report on tasks preempted in RCU read-side critical sections during * expedited RCU grace periods. */ static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp, bool wake) { } #endif /* #ifdef CONFIG_HOTPLUG_CPU */ /* * Because preemptible RCU does not exist, rcu_barrier() is just * another name for rcu_barrier_sched(). */ void rcu_barrier(void) { rcu_barrier_sched(); } EXPORT_SYMBOL_GPL(rcu_barrier); /* * Because preemptible RCU does not exist, it need not be initialized. */ static void __init __rcu_init_preempt(void) { } #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ #ifdef CONFIG_RCU_BOOST #include "rtmutex_common.h" #ifdef CONFIG_RCU_TRACE static void rcu_initiate_boost_trace(struct rcu_node *rnp) { if (list_empty(&rnp->blkd_tasks)) rnp->n_balk_blkd_tasks++; else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL) rnp->n_balk_exp_gp_tasks++; else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL) rnp->n_balk_boost_tasks++; else if (rnp->gp_tasks != NULL && rnp->qsmask != 0) rnp->n_balk_notblocked++; else if (rnp->gp_tasks != NULL && ULONG_CMP_LT(jiffies, rnp->boost_time)) rnp->n_balk_notyet++; else rnp->n_balk_nos++; } #else /* #ifdef CONFIG_RCU_TRACE */ static void rcu_initiate_boost_trace(struct rcu_node *rnp) { } #endif /* #else #ifdef CONFIG_RCU_TRACE */ static void rcu_wake_cond(struct task_struct *t, int status) { /* * If the thread is yielding, only wake it when this * is invoked from idle */ if (status != RCU_KTHREAD_YIELDING || is_idle_task(current)) wake_up_process(t); } /* * Carry out RCU priority boosting on the task indicated by ->exp_tasks * or ->boost_tasks, advancing the pointer to the next task in the * ->blkd_tasks list. * * Note that irqs must be enabled: boosting the task can block. * Returns 1 if there are more tasks needing to be boosted. */ static int rcu_boost(struct rcu_node *rnp) { unsigned long flags; struct rt_mutex mtx; struct task_struct *t; struct list_head *tb; if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) return 0; /* Nothing left to boost. */ raw_spin_lock_irqsave(&rnp->lock, flags); /* * Recheck under the lock: all tasks in need of boosting * might exit their RCU read-side critical sections on their own. */ if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) { raw_spin_unlock_irqrestore(&rnp->lock, flags); return 0; } /* * Preferentially boost tasks blocking expedited grace periods. * This cannot starve the normal grace periods because a second * expedited grace period must boost all blocked tasks, including * those blocking the pre-existing normal grace period. */ if (rnp->exp_tasks != NULL) { tb = rnp->exp_tasks; rnp->n_exp_boosts++; } else { tb = rnp->boost_tasks; rnp->n_normal_boosts++; } rnp->n_tasks_boosted++; /* * We boost task t by manufacturing an rt_mutex that appears to * be held by task t. We leave a pointer to that rt_mutex where * task t can find it, and task t will release the mutex when it * exits its outermost RCU read-side critical section. Then * simply acquiring this artificial rt_mutex will boost task * t's priority. (Thanks to tglx for suggesting this approach!) * * Note that task t must acquire rnp->lock to remove itself from * the ->blkd_tasks list, which it will do from exit() if from * nowhere else. We therefore are guaranteed that task t will * stay around at least until we drop rnp->lock. Note that * rnp->lock also resolves races between our priority boosting * and task t's exiting its outermost RCU read-side critical * section. */ t = container_of(tb, struct task_struct, rcu_node_entry); rt_mutex_init_proxy_locked(&mtx, t); t->rcu_boost_mutex = &mtx; raw_spin_unlock_irqrestore(&rnp->lock, flags); rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */ rt_mutex_unlock(&mtx); /* Keep lockdep happy. */ return ACCESS_ONCE(rnp->exp_tasks) != NULL || ACCESS_ONCE(rnp->boost_tasks) != NULL; } /* * Priority-boosting kthread. One per leaf rcu_node and one for the * root rcu_node. */ static int rcu_boost_kthread(void *arg) { struct rcu_node *rnp = (struct rcu_node *)arg; int spincnt = 0; int more2boost; trace_rcu_utilization("Start boost kthread@init"); for (;;) { rnp->boost_kthread_status = RCU_KTHREAD_WAITING; trace_rcu_utilization("End boost kthread@rcu_wait"); rcu_wait(rnp->boost_tasks || rnp->exp_tasks); trace_rcu_utilization("Start boost kthread@rcu_wait"); rnp->boost_kthread_status = RCU_KTHREAD_RUNNING; more2boost = rcu_boost(rnp); if (more2boost) spincnt++; else spincnt = 0; if (spincnt > 10) { rnp->boost_kthread_status = RCU_KTHREAD_YIELDING; trace_rcu_utilization("End boost kthread@rcu_yield"); schedule_timeout_interruptible(2); trace_rcu_utilization("Start boost kthread@rcu_yield"); spincnt = 0; } } /* NOTREACHED */ trace_rcu_utilization("End boost kthread@notreached"); return 0; } /* * Check to see if it is time to start boosting RCU readers that are * blocking the current grace period, and, if so, tell the per-rcu_node * kthread to start boosting them. If there is an expedited grace * period in progress, it is always time to boost. * * The caller must hold rnp->lock, which this function releases. * The ->boost_kthread_task is immortal, so we don't need to worry * about it going away. */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) { struct task_struct *t; if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) { rnp->n_balk_exp_gp_tasks++; raw_spin_unlock_irqrestore(&rnp->lock, flags); return; } if (rnp->exp_tasks != NULL || (rnp->gp_tasks != NULL && rnp->boost_tasks == NULL && rnp->qsmask == 0 && ULONG_CMP_GE(jiffies, rnp->boost_time))) { if (rnp->exp_tasks == NULL) rnp->boost_tasks = rnp->gp_tasks; raw_spin_unlock_irqrestore(&rnp->lock, flags); t = rnp->boost_kthread_task; if (t) rcu_wake_cond(t, rnp->boost_kthread_status); } else { rcu_initiate_boost_trace(rnp); raw_spin_unlock_irqrestore(&rnp->lock, flags); } } /* * Wake up the per-CPU kthread to invoke RCU callbacks. */ static void invoke_rcu_callbacks_kthread(void) { unsigned long flags; local_irq_save(flags); __this_cpu_write(rcu_cpu_has_work, 1); if (__this_cpu_read(rcu_cpu_kthread_task) != NULL && current != __this_cpu_read(rcu_cpu_kthread_task)) { rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task), __this_cpu_read(rcu_cpu_kthread_status)); } local_irq_restore(flags); } /* * Is the current CPU running the RCU-callbacks kthread? * Caller must have preemption disabled. */ static bool rcu_is_callbacks_kthread(void) { return __get_cpu_var(rcu_cpu_kthread_task) == current; } #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000) /* * Do priority-boost accounting for the start of a new grace period. */ static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) { rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES; } /* * Create an RCU-boost kthread for the specified node if one does not * already exist. We only create this kthread for preemptible RCU. * Returns zero if all is well, a negated errno otherwise. */ static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp, struct rcu_node *rnp) { int rnp_index = rnp - &rsp->node[0]; unsigned long flags; struct sched_param sp; struct task_struct *t; if (&rcu_preempt_state != rsp) return 0; if (!rcu_scheduler_fully_active || rnp->qsmaskinit == 0) return 0; rsp->boost = 1; if (rnp->boost_kthread_task != NULL) return 0; t = kthread_create(rcu_boost_kthread, (void *)rnp, "rcub/%d", rnp_index); if (IS_ERR(t)) return PTR_ERR(t); raw_spin_lock_irqsave(&rnp->lock, flags); rnp->boost_kthread_task = t; raw_spin_unlock_irqrestore(&rnp->lock, flags); sp.sched_priority = RCU_BOOST_PRIO; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */ return 0; } static void rcu_kthread_do_work(void) { rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data)); rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); rcu_preempt_do_callbacks(); } static void rcu_cpu_kthread_setup(unsigned int cpu) { struct sched_param sp; sp.sched_priority = RCU_KTHREAD_PRIO; sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); } static void rcu_cpu_kthread_park(unsigned int cpu) { per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU; } static int rcu_cpu_kthread_should_run(unsigned int cpu) { return __get_cpu_var(rcu_cpu_has_work); } /* * Per-CPU kernel thread that invokes RCU callbacks. This replaces the * RCU softirq used in flavors and configurations of RCU that do not * support RCU priority boosting. */ static void rcu_cpu_kthread(unsigned int cpu) { unsigned int *statusp = &__get_cpu_var(rcu_cpu_kthread_status); char work, *workp = &__get_cpu_var(rcu_cpu_has_work); int spincnt; for (spincnt = 0; spincnt < 10; spincnt++) { trace_rcu_utilization("Start CPU kthread@rcu_wait"); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; this_cpu_inc(rcu_cpu_kthread_loops); local_irq_disable(); work = *workp; *workp = 0; local_irq_enable(); if (work) rcu_kthread_do_work(); local_bh_enable(); if (*workp == 0) { trace_rcu_utilization("End CPU kthread@rcu_wait"); *statusp = RCU_KTHREAD_WAITING; return; } } *statusp = RCU_KTHREAD_YIELDING; trace_rcu_utilization("Start CPU kthread@rcu_yield"); schedule_timeout_interruptible(2); trace_rcu_utilization("End CPU kthread@rcu_yield"); *statusp = RCU_KTHREAD_WAITING; } /* * Set the per-rcu_node kthread's affinity to cover all CPUs that are * served by the rcu_node in question. The CPU hotplug lock is still * held, so the value of rnp->qsmaskinit will be stable. * * We don't include outgoingcpu in the affinity set, use -1 if there is * no outgoing CPU. If there are no CPUs left in the affinity set, * this function allows the kthread to execute on any CPU. */ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { struct task_struct *t = rnp->boost_kthread_task; unsigned long mask = rnp->qsmaskinit; cpumask_var_t cm; int cpu; if (!t) return; if (!zalloc_cpumask_var(&cm, GFP_KERNEL)) return; for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) if ((mask & 0x1) && cpu != outgoingcpu) cpumask_set_cpu(cpu, cm); if (cpumask_weight(cm) == 0) { cpumask_setall(cm); for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++) cpumask_clear_cpu(cpu, cm); WARN_ON_ONCE(cpumask_weight(cm) == 0); } set_cpus_allowed_ptr(t, cm); free_cpumask_var(cm); } static struct smp_hotplug_thread rcu_cpu_thread_spec = { .store = &rcu_cpu_kthread_task, .thread_should_run = rcu_cpu_kthread_should_run, .thread_fn = rcu_cpu_kthread, .thread_comm = "rcuc/%u", .setup = rcu_cpu_kthread_setup, .park = rcu_cpu_kthread_park, }; /* * Spawn all kthreads -- called as soon as the scheduler is running. */ static int __init rcu_spawn_kthreads(void) { struct rcu_node *rnp; int cpu; rcu_scheduler_fully_active = 1; for_each_possible_cpu(cpu) per_cpu(rcu_cpu_has_work, cpu) = 0; BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec)); rnp = rcu_get_root(rcu_state); (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); if (NUM_RCU_NODES > 1) { rcu_for_each_leaf_node(rcu_state, rnp) (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); } return 0; } early_initcall(rcu_spawn_kthreads); static void __cpuinit rcu_prepare_kthreads(int cpu) { struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu); struct rcu_node *rnp = rdp->mynode; /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */ if (rcu_scheduler_fully_active) (void)rcu_spawn_one_boost_kthread(rcu_state, rnp); } #else /* #ifdef CONFIG_RCU_BOOST */ static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags) { raw_spin_unlock_irqrestore(&rnp->lock, flags); } static void invoke_rcu_callbacks_kthread(void) { WARN_ON_ONCE(1); } static bool rcu_is_callbacks_kthread(void) { return false; } static void rcu_preempt_boost_start_gp(struct rcu_node *rnp) { } static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu) { } static int __init rcu_scheduler_really_started(void) { rcu_scheduler_fully_active = 1; return 0; } early_initcall(rcu_scheduler_really_started); static void __cpuinit rcu_prepare_kthreads(int cpu) { } #endif /* #else #ifdef CONFIG_RCU_BOOST */ #if !defined(CONFIG_RCU_FAST_NO_HZ) /* * Check to see if any future RCU-related work will need to be done * by the current CPU, even if none need be done immediately, returning * 1 if so. This function is part of the RCU implementation; it is -not- * an exported member of the RCU API. * * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs * any flavor of RCU. */ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) { *delta_jiffies = ULONG_MAX; return rcu_cpu_has_callbacks(cpu); } /* * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it. */ static void rcu_prepare_for_idle_init(int cpu) { } /* * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up * after it. */ static void rcu_cleanup_after_idle(int cpu) { } /* * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n, * is nothing. */ static void rcu_prepare_for_idle(int cpu) { } /* * Don't bother keeping a running count of the number of RCU callbacks * posted because CONFIG_RCU_FAST_NO_HZ=n. */ static void rcu_idle_count_callbacks_posted(void) { } #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ /* * This code is invoked when a CPU goes idle, at which point we want * to have the CPU do everything required for RCU so that it can enter * the energy-efficient dyntick-idle mode. This is handled by a * state machine implemented by rcu_prepare_for_idle() below. * * The following three proprocessor symbols control this state machine: * * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt * to satisfy RCU. Beyond this point, it is better to incur a periodic * scheduling-clock interrupt than to loop through the state machine * at full power. * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are * optional if RCU does not need anything immediately from this * CPU, even if this CPU still has RCU callbacks queued. The first * times through the state machine are mandatory: we need to give * the state machine a chance to communicate a quiescent state * to the RCU core. * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted * to sleep in dyntick-idle mode with RCU callbacks pending. This * is sized to be roughly one RCU grace period. Those energy-efficiency * benchmarkers who might otherwise be tempted to set this to a large * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your * system. And if you are -that- concerned about energy efficiency, * just power the system down and be done with it! * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is * permitted to sleep in dyntick-idle mode with only lazy RCU * callbacks pending. Setting this too high can OOM your system. * * The values below work well in practice. If future workloads require * adjustment, they can be converted into kernel config parameters, though * making the state machine smarter might be a better option. */ #define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */ #define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */ #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */ #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */ extern int tick_nohz_enabled; /* * Does the specified flavor of RCU have non-lazy callbacks pending on * the specified CPU? Both RCU flavor and CPU are specified by the * rcu_data structure. */ static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp) { return rdp->qlen != rdp->qlen_lazy; } #ifdef CONFIG_TREE_PREEMPT_RCU /* * Are there non-lazy RCU-preempt callbacks? (There cannot be if there * is no RCU-preempt in the kernel.) */ static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu); return __rcu_cpu_has_nonlazy_callbacks(rdp); } #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu) { return 0; } #endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */ /* * Does any flavor of RCU have non-lazy callbacks on the specified CPU? */ static bool rcu_cpu_has_nonlazy_callbacks(int cpu) { return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) || __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) || rcu_preempt_cpu_has_nonlazy_callbacks(cpu); } /* * Allow the CPU to enter dyntick-idle mode if either: (1) There are no * callbacks on this CPU, (2) this CPU has not yet attempted to enter * dyntick-idle mode, or (3) this CPU is in the process of attempting to * enter dyntick-idle mode. Otherwise, if we have recently tried and failed * to enter dyntick-idle mode, we refuse to try to enter it. After all, * it is better to incur scheduling-clock interrupts than to spin * continuously for the same time duration! * * The delta_jiffies argument is used to store the time when RCU is * going to need the CPU again if it still has callbacks. The reason * for this is that rcu_prepare_for_idle() might need to post a timer, * but if so, it will do so after tick_nohz_stop_sched_tick() has set * the wakeup time for this CPU. This means that RCU's timer can be * delayed until the wakeup time, which defeats the purpose of posting * a timer. */ int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); /* Flag a new idle sojourn to the idle-entry state machine. */ rdtp->idle_first_pass = 1; /* If no callbacks, RCU doesn't need the CPU. */ if (!rcu_cpu_has_callbacks(cpu)) { *delta_jiffies = ULONG_MAX; return 0; } if (rdtp->dyntick_holdoff == jiffies) { /* RCU recently tried and failed, so don't try again. */ *delta_jiffies = 1; return 1; } /* Set up for the possibility that RCU will post a timer. */ if (rcu_cpu_has_nonlazy_callbacks(cpu)) { *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies, RCU_IDLE_GP_DELAY) - jiffies; } else { *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY; *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies; } return 0; } /* * Handler for smp_call_function_single(). The only point of this * handler is to wake the CPU up, so the handler does only tracing. */ void rcu_idle_demigrate(void *unused) { trace_rcu_prep_idle("Demigrate"); } /* * Timer handler used to force CPU to start pushing its remaining RCU * callbacks in the case where it entered dyntick-idle mode with callbacks * pending. The hander doesn't really need to do anything because the * real work is done upon re-entry to idle, or by the next scheduling-clock * interrupt should idle not be re-entered. * * One special case: the timer gets migrated without awakening the CPU * on which the timer was scheduled on. In this case, we must wake up * that CPU. We do so with smp_call_function_single(). */ static void rcu_idle_gp_timer_func(unsigned long cpu_in) { int cpu = (int)cpu_in; trace_rcu_prep_idle("Timer"); if (cpu != smp_processor_id()) smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0); else WARN_ON_ONCE(1); /* Getting here can hang the system... */ } /* * Initialize the timer used to pull CPUs out of dyntick-idle mode. */ static void rcu_prepare_for_idle_init(int cpu) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); rdtp->dyntick_holdoff = jiffies - 1; setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu); rdtp->idle_gp_timer_expires = jiffies - 1; rdtp->idle_first_pass = 1; } /* * Clean up for exit from idle. Because we are exiting from idle, there * is no longer any point to ->idle_gp_timer, so cancel it. This will * do nothing if this timer is not active, so just cancel it unconditionally. */ static void rcu_cleanup_after_idle(int cpu) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); del_timer(&rdtp->idle_gp_timer); trace_rcu_prep_idle("Cleanup after idle"); rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled); } /* * Check to see if any RCU-related work can be done by the current CPU, * and if so, schedule a softirq to get it done. This function is part * of the RCU implementation; it is -not- an exported member of the RCU API. * * The idea is for the current CPU to clear out all work required by the * RCU core for the current grace period, so that this CPU can be permitted * to enter dyntick-idle mode. In some cases, it will need to be awakened * at the end of the grace period by whatever CPU ends the grace period. * This allows CPUs to go dyntick-idle more quickly, and to reduce the * number of wakeups by a modest integer factor. * * Because it is not legal to invoke rcu_process_callbacks() with irqs * disabled, we do one pass of force_quiescent_state(), then do a * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked * later. The ->dyntick_drain field controls the sequencing. * * The caller must have disabled interrupts. */ static void rcu_prepare_for_idle(int cpu) { struct timer_list *tp; struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); int tne; /* Handle nohz enablement switches conservatively. */ tne = ACCESS_ONCE(tick_nohz_enabled); if (tne != rdtp->tick_nohz_enabled_snap) { if (rcu_cpu_has_callbacks(cpu)) invoke_rcu_core(); /* force nohz to see update. */ rdtp->tick_nohz_enabled_snap = tne; return; } if (!tne) return; /* Adaptive-tick mode, where usermode execution is idle to RCU. */ if (!is_idle_task(current)) { rdtp->dyntick_holdoff = jiffies - 1; if (rcu_cpu_has_nonlazy_callbacks(cpu)) { trace_rcu_prep_idle("User dyntick with callbacks"); rdtp->idle_gp_timer_expires = round_up(jiffies + RCU_IDLE_GP_DELAY, RCU_IDLE_GP_DELAY); } else if (rcu_cpu_has_callbacks(cpu)) { rdtp->idle_gp_timer_expires = round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); trace_rcu_prep_idle("User dyntick with lazy callbacks"); } else { return; } tp = &rdtp->idle_gp_timer; mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); return; } /* * If this is an idle re-entry, for example, due to use of * RCU_NONIDLE() or the new idle-loop tracing API within the idle * loop, then don't take any state-machine actions, unless the * momentary exit from idle queued additional non-lazy callbacks. * Instead, repost the ->idle_gp_timer if this CPU has callbacks * pending. */ if (!rdtp->idle_first_pass && (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) { if (rcu_cpu_has_callbacks(cpu)) { tp = &rdtp->idle_gp_timer; mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); } return; } rdtp->idle_first_pass = 0; rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1; /* * If there are no callbacks on this CPU, enter dyntick-idle mode. * Also reset state to avoid prejudicing later attempts. */ if (!rcu_cpu_has_callbacks(cpu)) { rdtp->dyntick_holdoff = jiffies - 1; rdtp->dyntick_drain = 0; trace_rcu_prep_idle("No callbacks"); return; } /* * If in holdoff mode, just return. We will presumably have * refrained from disabling the scheduling-clock tick. */ if (rdtp->dyntick_holdoff == jiffies) { trace_rcu_prep_idle("In holdoff"); return; } /* Check and update the ->dyntick_drain sequencing. */ if (rdtp->dyntick_drain <= 0) { /* First time through, initialize the counter. */ rdtp->dyntick_drain = RCU_IDLE_FLUSHES; } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES && !rcu_pending(cpu) && !local_softirq_pending()) { /* Can we go dyntick-idle despite still having callbacks? */ rdtp->dyntick_drain = 0; rdtp->dyntick_holdoff = jiffies; if (rcu_cpu_has_nonlazy_callbacks(cpu)) { trace_rcu_prep_idle("Dyntick with callbacks"); rdtp->idle_gp_timer_expires = round_up(jiffies + RCU_IDLE_GP_DELAY, RCU_IDLE_GP_DELAY); } else { rdtp->idle_gp_timer_expires = round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY); trace_rcu_prep_idle("Dyntick with lazy callbacks"); } tp = &rdtp->idle_gp_timer; mod_timer_pinned(tp, rdtp->idle_gp_timer_expires); rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted; return; /* Nothing more to do immediately. */ } else if (--(rdtp->dyntick_drain) <= 0) { /* We have hit the limit, so time to give up. */ rdtp->dyntick_holdoff = jiffies; trace_rcu_prep_idle("Begin holdoff"); invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */ return; } /* * Do one step of pushing the remaining RCU callbacks through * the RCU core state machine. */ #ifdef CONFIG_TREE_PREEMPT_RCU if (per_cpu(rcu_preempt_data, cpu).nxtlist) { rcu_preempt_qs(cpu); force_quiescent_state(&rcu_preempt_state); } #endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */ if (per_cpu(rcu_sched_data, cpu).nxtlist) { rcu_sched_qs(cpu); force_quiescent_state(&rcu_sched_state); } if (per_cpu(rcu_bh_data, cpu).nxtlist) { rcu_bh_qs(cpu); force_quiescent_state(&rcu_bh_state); } /* * If RCU callbacks are still pending, RCU still needs this CPU. * So try forcing the callbacks through the grace period. */ if (rcu_cpu_has_callbacks(cpu)) { trace_rcu_prep_idle("More callbacks"); invoke_rcu_core(); } else { trace_rcu_prep_idle("Callbacks drained"); } } /* * Keep a running count of the number of non-lazy callbacks posted * on this CPU. This running counter (which is never decremented) allows * rcu_prepare_for_idle() to detect when something out of the idle loop * posts a callback, even if an equal number of callbacks are invoked. * Of course, callbacks should only be posted from within a trace event * designed to be called from idle or from within RCU_NONIDLE(). */ static void rcu_idle_count_callbacks_posted(void) { __this_cpu_add(rcu_dynticks.nonlazy_posted, 1); } /* * Data for flushing lazy RCU callbacks at OOM time. */ static atomic_t oom_callback_count; static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq); /* * RCU OOM callback -- decrement the outstanding count and deliver the * wake-up if we are the last one. */ static void rcu_oom_callback(struct rcu_head *rhp) { if (atomic_dec_and_test(&oom_callback_count)) wake_up(&oom_callback_wq); } /* * Post an rcu_oom_notify callback on the current CPU if it has at * least one lazy callback. This will unnecessarily post callbacks * to CPUs that already have a non-lazy callback at the end of their * callback list, but this is an infrequent operation, so accept some * extra overhead to keep things simple. */ static void rcu_oom_notify_cpu(void *unused) { struct rcu_state *rsp; struct rcu_data *rdp; for_each_rcu_flavor(rsp) { rdp = __this_cpu_ptr(rsp->rda); if (rdp->qlen_lazy != 0) { atomic_inc(&oom_callback_count); rsp->call(&rdp->oom_head, rcu_oom_callback); } } } /* * If low on memory, ensure that each CPU has a non-lazy callback. * This will wake up CPUs that have only lazy callbacks, in turn * ensuring that they free up the corresponding memory in a timely manner. * Because an uncertain amount of memory will be freed in some uncertain * timeframe, we do not claim to have freed anything. */ static int rcu_oom_notify(struct notifier_block *self, unsigned long notused, void *nfreed) { int cpu; /* Wait for callbacks from earlier instance to complete. */ wait_event(oom_callback_wq, atomic_read(&oom_callback_count) == 0); /* * Prevent premature wakeup: ensure that all increments happen * before there is a chance of the counter reaching zero. */ atomic_set(&oom_callback_count, 1); get_online_cpus(); for_each_online_cpu(cpu) { smp_call_function_single(cpu, rcu_oom_notify_cpu, NULL, 1); cond_resched(); } put_online_cpus(); /* Unconditionally decrement: no need to wake ourselves up. */ atomic_dec(&oom_callback_count); return NOTIFY_OK; } static struct notifier_block rcu_oom_nb = { .notifier_call = rcu_oom_notify }; static int __init rcu_register_oom_notifier(void) { register_oom_notifier(&rcu_oom_nb); return 0; } early_initcall(rcu_register_oom_notifier); #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ #ifdef CONFIG_RCU_CPU_STALL_INFO #ifdef CONFIG_RCU_FAST_NO_HZ static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); struct timer_list *tltp = &rdtp->idle_gp_timer; char c; c = rdtp->dyntick_holdoff == jiffies ? 'H' : '.'; if (timer_pending(tltp)) sprintf(cp, "drain=%d %c timer=%lu", rdtp->dyntick_drain, c, tltp->expires - jiffies); else sprintf(cp, "drain=%d %c timer not pending", rdtp->dyntick_drain, c); } #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */ static void print_cpu_stall_fast_no_hz(char *cp, int cpu) { *cp = '\0'; } #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */ /* Initiate the stall-info list. */ static void print_cpu_stall_info_begin(void) { printk(KERN_CONT "\n"); } /* * Print out diagnostic information for the specified stalled CPU. * * If the specified CPU is aware of the current RCU grace period * (flavor specified by rsp), then print the number of scheduling * clock interrupts the CPU has taken during the time that it has * been aware. Otherwise, print the number of RCU grace periods * that this CPU is ignorant of, for example, "1" if the CPU was * aware of the previous grace period. * * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info. */ static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) { char fast_no_hz[72]; struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); struct rcu_dynticks *rdtp = rdp->dynticks; char *ticks_title; unsigned long ticks_value; if (rsp->gpnum == rdp->gpnum) { ticks_title = "ticks this GP"; ticks_value = rdp->ticks_this_gp; } else { ticks_title = "GPs behind"; ticks_value = rsp->gpnum - rdp->gpnum; } print_cpu_stall_fast_no_hz(fast_no_hz, cpu); printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n", cpu, ticks_value, ticks_title, atomic_read(&rdtp->dynticks) & 0xfff, rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting, fast_no_hz); } /* Terminate the stall-info list. */ static void print_cpu_stall_info_end(void) { printk(KERN_ERR "\t"); } /* Zero ->ticks_this_gp for all flavors of RCU. */ static void zero_cpu_stall_ticks(struct rcu_data *rdp) { rdp->ticks_this_gp = 0; } /* Increment ->ticks_this_gp for all flavors of RCU. */ static void increment_cpu_stall_ticks(void) { struct rcu_state *rsp; for_each_rcu_flavor(rsp) __this_cpu_ptr(rsp->rda)->ticks_this_gp++; } #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */ static void print_cpu_stall_info_begin(void) { printk(KERN_CONT " {"); } static void print_cpu_stall_info(struct rcu_state *rsp, int cpu) { printk(KERN_CONT " %d", cpu); } static void print_cpu_stall_info_end(void) { printk(KERN_CONT "} "); } static void zero_cpu_stall_ticks(struct rcu_data *rdp) { } static void increment_cpu_stall_ticks(void) { } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */