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Commit be45bf53 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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watchdog/softlockup: Fix cpu_stop_queue_work() double-queue bug 



When scheduling is delayed for longer than the softlockup interrupt
period it is possible to double-queue the cpu_stop_work, causing list
corruption.

Cure this by adding a completion to track the cpu_stop_work's
progress.

Reported-by: default avatarkernel test robot <lkp@intel.com>
Tested-by: default avatarRong Chen <rong.a.chen@intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 9cf57731 ("watchdog/softlockup: Replace "watchdog/%u" threads with cpu_stop_work")
Link: http://lkml.kernel.org/r/20180713104208.GW2494@hirez.programming.kicks-ass.net


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent fdf2ceb7

kernel/watchdog.c

+15 −5
Original line number Diff line number Diff line
@@ -330,6 +330,9 @@ static void watchdog_interrupt_count(void) 
	__this_cpu_inc(hrtimer_interrupts);

}



static DEFINE_PER_CPU(struct completion, softlockup_completion);

static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);



/*

 * The watchdog thread function - touches the timestamp.

 *
@@ -343,12 +346,11 @@ static int softlockup_fn(void *data) 
	__this_cpu_write(soft_lockup_hrtimer_cnt,

			 __this_cpu_read(hrtimer_interrupts));

	__touch_watchdog();

	complete(this_cpu_ptr(&softlockup_completion));



	return 0;

}



static DEFINE_PER_CPU(struct cpu_stop_work, softlockup_stop_work);



/* watchdog kicker functions */

static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)

{
@@ -364,9 +366,12 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 
	watchdog_interrupt_count();



	/* kick the softlockup detector */

	if (completion_done(this_cpu_ptr(&softlockup_completion))) {

		reinit_completion(this_cpu_ptr(&softlockup_completion));

		stop_one_cpu_nowait(smp_processor_id(),

				softlockup_fn, NULL,

				this_cpu_ptr(&softlockup_stop_work));

	}



	/* .. and repeat */

	hrtimer_forward_now(hrtimer, ns_to_ktime(sample_period));
@@ -467,9 +472,13 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer) 
static void watchdog_enable(unsigned int cpu)

{

	struct hrtimer *hrtimer = this_cpu_ptr(&watchdog_hrtimer);

	struct completion *done = this_cpu_ptr(&softlockup_completion);



	WARN_ON_ONCE(cpu != smp_processor_id());



	init_completion(done);

	complete(done);



	/*

	 * Start the timer first to prevent the NMI watchdog triggering

	 * before the timer has a chance to fire.
@@ -499,6 +508,7 @@ static void watchdog_disable(unsigned int cpu) 
	 */

	watchdog_nmi_disable(cpu);

	hrtimer_cancel(hrtimer);

	wait_for_completion(this_cpu_ptr(&softlockup_completion));

}



static int softlockup_stop_fn(void *data)