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cpu/hotplug: Plug death reporting race 

Paul noticed that the conversion of the death reporting introduced a race
where the outgoing cpu might be delayed after waking the controll processor,
so it might not be able to call rcu_report_dead() before being physically
removed, leading to RCU stalls.

We cant call complete after rcu_report_dead(), so instead of going back to
busy polling, simply issue a function call to do the completion.

Fixes: 27d50c7eeb "rcu: Make CPU_DYING_IDLE an explicit call"
Reported-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Link: http://lkml.kernel.org/r/20160302201127.GA23440@linux.vnet.ibm.com
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra <peterz@infradead.org>
This commit is contained in:
Thomas Gleixner 2016-03-03 10:52:10 +01:00
parent 27d50c7eeb
commit 71f87b2fc6
1 changed files with 14 additions and 2 deletions
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16
kernel/cpu.c
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@ -755,14 +755,26 @@ static int notify_dead(unsigned int cpu)
return 0; return 0;
} }
static void cpuhp_complete_idle_dead(void *arg)
{
struct cpuhp_cpu_state *st = arg;
complete(&st->done);
}
void cpuhp_report_idle_dead(void) void cpuhp_report_idle_dead(void)
{ {
struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state); struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);
BUG_ON(st->state != CPUHP_AP_OFFLINE); BUG_ON(st->state != CPUHP_AP_OFFLINE);
st->state = CPUHP_AP_IDLE_DEAD;
complete(&st->done);
rcu_report_dead(smp_processor_id()); rcu_report_dead(smp_processor_id());
st->state = CPUHP_AP_IDLE_DEAD;
/*
* We cannot call complete after rcu_report_dead() so we delegate it
* to an online cpu.
*/
smp_call_function_single(cpumask_first(cpu_online_mask),
cpuhp_complete_idle_dead, st, 0);
} }
#else #else