On Tue, Aug 26, 2014 at 08:51:30PM +0800, Chai Wen wrote:
> On 08/22/2014 09:58 AM, Don Zickus wrote:
>
> > On Thu, Aug 21, 2014 at 01:42:22PM +0800, 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>
> >
> > Acked-by: Don Zickus <dzic...@redhat.com>
> >
>
>
> Hi Andrew
>
> Sorry for some disturbing.
> Could you help to check and pick up this little improvement patch ?
>
> I am not sure which MAINTAINER I should talk to, but the original version of
> this patch is queued to -mm tree by you, so I assume that they are in the
> charge of you.
>
>
> thanks
> chai wen
Hi Chai,
Sorry about that. Ingo asked me privately to pick this up and re-post
with my signoff. I was converting to a new test env and was going to use this
patch as an excuse to exercise it. That is the delay. Let me get this
out today.
Cheers,
Don
>
> >> ---
> >> 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)
> >> --
> >> 1.7.1
> >>
> > .
> >
>
>
>
> --
> Regards
>
> Chai Wen
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