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rcu: Eliminate RCU_FAST_NO_HZ grace-period hang

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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 <[email protected]>
Signed-off-by: Paul E. McKenney <[email protected]>
This commit is contained in:
Paul E. McKenney 2011-11-22 20:43:02 -08:00 • committed by Paul E. McKenney
commit f535a607c1
4 changed files with 2 additions and 82 deletions
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3
kernel/rcutree.h
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@ -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 */