diff options
author | Paul E. McKenney <paul.mckenney@linaro.org> | 2011-11-23 08:43:02 +0400 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2011-12-11 22:32:02 +0400 |
commit | f535a607c13c7b674e0788ca5765779aa74a01c3 (patch) | |
tree | 433a07d16ff11d9f67e7991831cebf3cadfd9939 /kernel | |
parent | 84ad00cb61f1cb21f0b63bc6f7dc254399eb3830 (diff) | |
download | linux-f535a607c13c7b674e0788ca5765779aa74a01c3.tar.xz |
rcu: Eliminate RCU_FAST_NO_HZ grace-period hang
With the new implementation of RCU_FAST_NO_HZ, it was possible to hang
RCU grace periods as follows:
o CPU 0 attempts to go idle, cycles several times through the
rcu_prepare_for_idle() loop, then goes dyntick-idle when
RCU needs nothing more from it, while still having at least
on RCU callback pending.
o CPU 1 goes idle with no callbacks.
Both CPUs can then stay in dyntick-idle mode indefinitely, preventing
the RCU grace period from ever completing, possibly hanging the system.
This commit therefore prevents CPUs that have RCU callbacks from entering
dyntick-idle mode. This approach also eliminates the need for the
end-of-grace-period IPIs used previously.
Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcutree.c | 2 | ||||
-rw-r--r-- | kernel/rcutree.h | 3 | ||||
-rw-r--r-- | kernel/rcutree_plugin.h | 78 |
3 files changed, 2 insertions, 81 deletions
diff --git a/kernel/rcutree.c b/kernel/rcutree.c index 7fb8b0e60811..13fab4a9f9fb 100644 --- a/kernel/rcutree.c +++ b/kernel/rcutree.c @@ -1086,7 +1086,6 @@ static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags) * callbacks are waiting on the grace period that just now * completed. */ - rcu_schedule_wake_gp_end(); if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) { raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ @@ -1672,7 +1671,6 @@ static void rcu_process_callbacks(struct softirq_action *unused) &__get_cpu_var(rcu_sched_data)); __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data)); rcu_preempt_process_callbacks(); - rcu_wake_cpus_for_gp_end(); trace_rcu_utilization("End RCU core"); } diff --git a/kernel/rcutree.h b/kernel/rcutree.h index ea32405177c9..70d8a557090f 100644 --- a/kernel/rcutree.h +++ b/kernel/rcutree.h @@ -88,7 +88,6 @@ struct rcu_dynticks { /* Process level is worth LLONG_MAX/2. */ int dynticks_nmi_nesting; /* Track NMI nesting level. */ atomic_t dynticks; /* Even value for idle, else odd. */ - int wake_gp_end; /* A GP ended, need to wake up CPUs. */ }; /* RCU's kthread states for tracing. */ @@ -469,7 +468,5 @@ static void rcu_yield(void (*f)(unsigned long), unsigned long arg); static void rcu_cpu_kthread_setrt(int cpu, int to_rt); static void __cpuinit rcu_prepare_kthreads(int cpu); static void rcu_prepare_for_idle(int cpu); -static void rcu_wake_cpus_for_gp_end(void); -static void rcu_schedule_wake_gp_end(void); #endif /* #ifndef RCU_TREE_NONCORE */ diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h index c4daf1e19e01..3d84dbc113d6 100644 --- a/kernel/rcutree_plugin.h +++ b/kernel/rcutree_plugin.h @@ -1964,28 +1964,11 @@ static void rcu_prepare_for_idle(int cpu) { } -/* - * CPUs are never putting themselves to sleep with callbacks pending, - * so there is no need to awaken them. - */ -static void rcu_wake_cpus_for_gp_end(void) -{ -} - -/* - * CPUs are never putting themselves to sleep with callbacks pending, - * so there is no need to schedule the act of awakening them. - */ -static void rcu_schedule_wake_gp_end(void) -{ -} - #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */ #define RCU_NEEDS_CPU_FLUSHES 5 static DEFINE_PER_CPU(int, rcu_dyntick_drain); static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff); -static DEFINE_PER_CPU(bool, rcu_awake_at_gp_end); /* * Allow the CPU to enter dyntick-idle mode if either: (1) There are no @@ -2032,26 +2015,16 @@ static void rcu_prepare_for_idle(int cpu) local_irq_save(flags); /* - * If there are no callbacks on this CPU or if RCU has no further - * need for this CPU at the moment, enter dyntick-idle mode. - * Also reset state so as to not prejudice later attempts. + * 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)) { per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; per_cpu(rcu_dyntick_drain, cpu) = 0; - per_cpu(rcu_awake_at_gp_end, cpu) = 0; local_irq_restore(flags); trace_rcu_prep_idle("No callbacks"); return; } - if (!rcu_pending(cpu)) { - per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1; - per_cpu(rcu_dyntick_drain, cpu) = 0; - per_cpu(rcu_awake_at_gp_end, cpu) = 1; - local_irq_restore(flags); - trace_rcu_prep_idle("Dyntick with callbacks"); - return; /* Nothing to do immediately. */ - } /* * If in holdoff mode, just return. We will presumably have @@ -2067,7 +2040,6 @@ static void rcu_prepare_for_idle(int cpu) if (per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* First time through, initialize the counter. */ per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES; - per_cpu(rcu_awake_at_gp_end, cpu) = 0; } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) { /* We have hit the limit, so time to give up. */ per_cpu(rcu_dyntick_holdoff, cpu) = jiffies; @@ -2113,50 +2085,4 @@ static void rcu_prepare_for_idle(int cpu) } } -/* - * Wake up a CPU by invoking the RCU core. Intended for use by - * rcu_wake_cpus_for_gp_end(), which passes this function to - * smp_call_function_single(). - */ -static void rcu_wake_cpu(void *unused) -{ - trace_rcu_prep_idle("CPU awakened at GP end"); - invoke_rcu_core(); -} - -/* - * If an RCU grace period ended recently, scan the rcu_awake_at_gp_end - * per-CPU variables, and wake up any CPUs that requested a wakeup. - */ -static void rcu_wake_cpus_for_gp_end(void) -{ - int cpu; - struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); - - if (!rdtp->wake_gp_end) - return; - rdtp->wake_gp_end = 0; - for_each_online_cpu(cpu) { - if (per_cpu(rcu_awake_at_gp_end, cpu)) { - per_cpu(rcu_awake_at_gp_end, cpu) = 0; - smp_call_function_single(cpu, rcu_wake_cpu, NULL, 0); - } - } -} - -/* - * A grace period has just ended, and so we will need to awaken CPUs - * that now have work to do. But we cannot send IPIs with interrupts - * disabled, so just set a flag so that this will happen upon exit - * from RCU core processing. - */ -static void rcu_schedule_wake_gp_end(void) -{ - struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks); - - rdtp->wake_gp_end = 1; -} - -/* @@@ need tracing as well. */ - #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */ |