diff options
Diffstat (limited to 'kernel/rcutree.c')
| -rw-r--r-- | kernel/rcutree.c | 229 |
1 files changed, 162 insertions, 67 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 5d0b55a3a8c0..1c40326724f6 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -195,12 +195,10 @@ void rcu_note_context_switch(int cpu) } EXPORT_SYMBOL_GPL(rcu_note_context_switch); -#ifdef CONFIG_NO_HZ DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { - .dynticks_nesting = 1, + .dynticks_nesting = LLONG_MAX / 2, .dynticks = ATOMIC_INIT(1), }; -#endif /* #ifdef CONFIG_NO_HZ */ static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */ static int qhimark = 10000; /* If this many pending, ignore blimit. */ @@ -328,11 +326,11 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) return 1; } - /* If preemptible RCU, no point in sending reschedule IPI. */ - if (rdp->preemptible) - return 0; - - /* The CPU is online, so send it a reschedule IPI. */ + /* + * The CPU is online, so send it a reschedule IPI. This forces + * it through the scheduler, and (inefficiently) also handles cases + * where idle loops fail to inform RCU about the CPU being idle. + */ if (rdp->cpu != smp_processor_id()) smp_send_reschedule(rdp->cpu); else @@ -343,51 +341,97 @@ static int rcu_implicit_offline_qs(struct rcu_data *rdp) #endif /* #ifdef CONFIG_SMP */ -#ifdef CONFIG_NO_HZ +/* + * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle + * + * 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_idle_enter_common(struct rcu_dynticks *rdtp) +{ + if (rdtp->dynticks_nesting) { + trace_rcu_dyntick("--=", rdtp->dynticks_nesting); + return; + } + trace_rcu_dyntick("Start", rdtp->dynticks_nesting); + if (!idle_cpu(smp_processor_id())) { + WARN_ON_ONCE(1); /* must be idle task! */ + trace_rcu_dyntick("Error on entry: not idle task", + rdtp->dynticks_nesting); + ftrace_dump(DUMP_ALL); + } + /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ + smp_mb__before_atomic_inc(); /* See above. */ + atomic_inc(&rdtp->dynticks); + smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */ + WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); +} /** - * rcu_enter_nohz - inform RCU that current CPU is entering nohz + * rcu_idle_enter - inform RCU that current CPU is entering idle * - * Enter nohz mode, in other words, -leave- the mode in which RCU + * 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 nohz mode, a possibility - * handled by rcu_irq_enter() and rcu_irq_exit()). + * 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_enter_nohz(void) +void rcu_idle_enter(void) { unsigned long flags; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); - if (--rdtp->dynticks_nesting) { - local_irq_restore(flags); - return; - } - trace_rcu_dyntick("Start"); - /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ - smp_mb__before_atomic_inc(); /* See above. */ - atomic_inc(&rdtp->dynticks); - smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */ - WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); + rdtp->dynticks_nesting = 0; + rcu_idle_enter_common(rdtp); local_irq_restore(flags); } -/* - * rcu_exit_nohz - inform RCU that current CPU is leaving nohz +/** + * 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. * - * Exit nohz mode, in other words, -enter- the mode in which RCU - * read-side critical sections normally 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_exit_nohz(void) +void rcu_irq_exit(void) { unsigned long flags; struct rcu_dynticks *rdtp; local_irq_save(flags); rdtp = &__get_cpu_var(rcu_dynticks); - if (rdtp->dynticks_nesting++) { - local_irq_restore(flags); + rdtp->dynticks_nesting--; + WARN_ON_ONCE(rdtp->dynticks_nesting < 0); + rcu_idle_enter_common(rdtp); + local_irq_restore(flags); +} + +/* + * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle + * + * 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_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval) +{ + if (oldval) { + trace_rcu_dyntick("++=", rdtp->dynticks_nesting); return; } smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */ @@ -395,7 +439,71 @@ void rcu_exit_nohz(void) /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ smp_mb__after_atomic_inc(); /* See above. */ WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); - trace_rcu_dyntick("End"); + trace_rcu_dyntick("End", oldval); + if (!idle_cpu(smp_processor_id())) { + WARN_ON_ONCE(1); /* must be idle task! */ + trace_rcu_dyntick("Error on exit: not idle task", oldval); + ftrace_dump(DUMP_ALL); + } +} + +/** + * 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 LLONG_MAX/2 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; + struct rcu_dynticks *rdtp; + long long oldval; + + local_irq_save(flags); + rdtp = &__get_cpu_var(rcu_dynticks); + oldval = rdtp->dynticks_nesting; + WARN_ON_ONCE(oldval != 0); + rdtp->dynticks_nesting = LLONG_MAX / 2; + rcu_idle_exit_common(rdtp, oldval); + local_irq_restore(flags); +} + +/** + * 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 = &__get_cpu_var(rcu_dynticks); + oldval = rdtp->dynticks_nesting; + rdtp->dynticks_nesting++; + WARN_ON_ONCE(rdtp->dynticks_nesting == 0); + rcu_idle_exit_common(rdtp, oldval); local_irq_restore(flags); } @@ -442,27 +550,32 @@ void rcu_nmi_exit(void) WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); } +#ifdef CONFIG_PROVE_RCU + /** - * rcu_irq_enter - inform RCU of entry to hard irq context + * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle * - * If the CPU was idle with dynamic ticks active, this updates the - * rdtp->dynticks to let the RCU handling know that the CPU is active. + * If the current CPU is in its idle loop and is neither in an interrupt + * or NMI handler, return true. The caller must have at least disabled + * preemption. */ -void rcu_irq_enter(void) +int rcu_is_cpu_idle(void) { - rcu_exit_nohz(); + return (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0; } +#endif /* #ifdef CONFIG_PROVE_RCU */ + /** - * rcu_irq_exit - inform RCU of exit from hard irq context + * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle * - * If the CPU was idle with dynamic ticks active, update the rdp->dynticks - * to put let the RCU handling be aware that the CPU is going back to idle - * with no ticks. + * 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. */ -void rcu_irq_exit(void) +int rcu_is_cpu_rrupt_from_idle(void) { - rcu_enter_nohz(); + return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1; } #ifdef CONFIG_SMP @@ -512,24 +625,6 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) #endif /* #ifdef CONFIG_SMP */ -#else /* #ifdef CONFIG_NO_HZ */ - -#ifdef CONFIG_SMP - -static int dyntick_save_progress_counter(struct rcu_data *rdp) -{ - return 0; -} - -static int rcu_implicit_dynticks_qs(struct rcu_data *rdp) -{ - return rcu_implicit_offline_qs(rdp); -} - -#endif /* #ifdef CONFIG_SMP */ - -#endif /* #else #ifdef CONFIG_NO_HZ */ - int rcu_cpu_stall_suppress __read_mostly; static void record_gp_stall_check_time(struct rcu_state *rsp) @@ -1334,16 +1429,14 @@ static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp) * (user mode or idle loop for rcu, non-softirq execution for rcu_bh). * Also schedule RCU core processing. * - * This function must be called with hardirqs disabled. It is normally + * 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 cpu, int user) { trace_rcu_utilization("Start scheduler-tick"); - if (user || - (idle_cpu(cpu) && rcu_scheduler_active && - !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) { + if (user || rcu_is_cpu_rrupt_from_idle()) { /* * Get here if this CPU took its interrupt from user @@ -1913,9 +2006,9 @@ rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp) for (i = 0; i < RCU_NEXT_SIZE; i++) rdp->nxttail[i] = &rdp->nxtlist; rdp->qlen = 0; -#ifdef CONFIG_NO_HZ rdp->dynticks = &per_cpu(rcu_dynticks, cpu); -#endif /* #ifdef CONFIG_NO_HZ */ + WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2); + WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1); rdp->cpu = cpu; rdp->rsp = rsp; raw_spin_unlock_irqrestore(&rnp->lock, flags); @@ -1942,6 +2035,8 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible) rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = rsp->n_force_qs; rdp->blimit = blimit; + WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != LLONG_MAX / 2); + WARN_ON_ONCE((atomic_read(&rdp->dynticks->dynticks) & 0x1) != 1); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ /* |