softlockup: make detector be aware of task switch of processes hogging cpu (b1a8de1f) · Commits · 戴 / test

For now, soft lockup detector warns once for each case of process softlockup. But the thread 'watchdog/n' may not always get the cpu at the time slot between the task switch of two processes hogging that cpu to reset soft_watchdog_warn. An example would be two processes hogging the cpu. Process A causes the softlockup warning and is killed manually by a user. Process B immediately becomes the new process hogging the cpu preventing the softlockup code from resetting the soft_watchdog_warn variable. This case is a false negative of "warn only once for a process", as there may be a different process that is going to hog the cpu. Resolve this by saving/checking the task pointer of the hogging process and use that to reset soft_watchdog_warn too. [dzickus@redhat.com: update comment] Signed-off-by:

chai wen <chaiw.fnst@cn.fujitsu.com> Signed-off-by:

Don Zickus <dzickus@redhat.com> Cc: Ingo Molnar <mingo@elte.hu> Signed-off-by:

Andrew Morton <akpm@linux-foundation.org> Signed-off-by:

Linus Torvalds <torvalds@linux-foundation.org>

kernel/watchdog.c

+17 −1

Original line number	Diff line number	Diff line
		@@ -47,6 +47,7 @@ static DEFINE_PER_CPU(bool, softlockup_touch_sync);
		static DEFINE_PER_CPU(bool, soft_watchdog_warn);
		static DEFINE_PER_CPU(unsigned long, hrtimer_interrupts);
		static DEFINE_PER_CPU(unsigned long, soft_lockup_hrtimer_cnt);
		static DEFINE_PER_CPU(struct task_struct *, softlockup_task_ptr_saved);
		#ifdef CONFIG_HARDLOCKUP_DETECTOR
		static DEFINE_PER_CPU(bool, hard_watchdog_warn);
		static DEFINE_PER_CPU(bool, watchdog_nmi_touch);
		@@ -333,8 +334,22 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
		return HRTIMER_RESTART;

		/* only warn once */
		if (__this_cpu_read(soft_watchdog_warn) == true)
		if (__this_cpu_read(soft_watchdog_warn) == true) {
		/*
		* When multiple processes are causing softlockups the
		* softlockup detector only warns on the first one
		* because the code relies on a full quiet cycle to
		* re-arm. The second process prevents the quiet cycle
		* and never gets reported. Use task pointers to detect
		* this.
		*/
		if (__this_cpu_read(softlockup_task_ptr_saved) !=
		current) {
		__this_cpu_write(soft_watchdog_warn, false);
		__touch_watchdog();
		}
		return HRTIMER_RESTART;
		}

		if (softlockup_all_cpu_backtrace) {
		/* Prevent multiple soft-lockup reports if one cpu is already
		@@ -350,6 +365,7 @@ static enum hrtimer_restart watchdog_timer_fn(struct hrtimer *hrtimer)
		pr_emerg("BUG: soft lockup - CPU#%d stuck for %us! [%s:%d]\n",
		smp_processor_id(), duration,
		current->comm, task_pid_nr(current));
		__this_cpu_write(softlockup_task_ptr_saved, current);
		print_modules();
		print_irqtrace_events(current);
		if (regs)

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