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Subject[tip:sched/core] watchdog/softlockup: Fix cpu_stop_queue_work() double-queue bug
Commit-ID:  be45bf5395e0886a93fc816bbe41a008ec2e42e2
Gitweb: https://git.kernel.org/tip/be45bf5395e0886a93fc816bbe41a008ec2e42e2
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Fri, 13 Jul 2018 12:42:08 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Sun, 15 Jul 2018 23:51:19 +0200

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: kernel test robot <lkp@intel.com>
Tested-by: Rong Chen <rong.a.chen@intel.com>
Signed-off-by: Peter 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: 9cf57731b63e ("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: Ingo Molnar <mingo@kernel.org>
---
kernel/watchdog.c | 20 +++++++++++++++-----
1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index b81f777838d5..5470dce212c0 100644
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -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 */
- stop_one_cpu_nowait(smp_processor_id(),
- softlockup_fn, NULL,
- this_cpu_ptr(&softlockup_stop_work));
+ 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)
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