On 08/21/2014 01:42 PM, chai wen wrote:
> 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.
>
> Signed-off-by: chai wen <chaiw.f...@cn.fujitsu.com>
> Signed-off-by: Don Zickus <dzic...@redhat.com>
Hi Ingo & Don
Ping...
This patch is using the task pointer to check cases that softlockup can
not reset itself, and has been tested.
thanks
chai wen
> ---
> kernel/watchdog.c | 16 +++++++++++++++-
> 1 files changed, 15 insertions(+), 1 deletions(-)
>
> diff --git a/kernel/watchdog.c b/kernel/watchdog.c
> index 0037db6..2e55620 100644
> --- a/kernel/watchdog.c
> +++ b/kernel/watchdog.c
> @@ -42,6 +42,7 @@ 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);
> @@ -328,8 +329,20 @@ 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) {
> + /*
> + * Handle the case where multiple processes are
> + * causing softlockups but the duration is small
> + * enough, the softlockup detector can not reset
> + * itself in time. 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
> @@ -345,6 +358,7 @@ 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)
--
Regards
Chai Wen
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