Commit 71f87b2f authored Mar 03, 2016 by Thomas Gleixner

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: 27d50c7e "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>

parent 27d50c7e

kernel/cpu.c

+14 −2

Original line number	Diff line number	Diff line
		@@ -755,14 +755,26 @@ static int notify_dead(unsigned int cpu)
		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)
		{
		struct cpuhp_cpu_state *st = this_cpu_ptr(&cpuhp_state);

		BUG_ON(st->state != CPUHP_AP_OFFLINE);
		st->state = CPUHP_AP_IDLE_DEAD;
		complete(&st->done);
		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