Re: [PATCH RESEND v3] perf/core: Fix hardlockup failure caused by perf throttle

[Yang Jihong]

Hello,

PING.

This patch has not been responded.
Please take time to check whether the fix solution is OK.
Look forward to reviewing the patch. Thanks :)

Thanks,
Yang.

On 2023/3/6 9:14, Yang Jihong wrote:
> Hello,
>
> PING.
>
> Thanks,
> Yang.
>
> On 2023/2/27 10:35, Yang Jihong wrote:
> > commit e050e3f0a71bf ("perf: Fix broken interrupt rate throttling")
> > introduces a change in throttling threshold judgment. Before this,
> > compare hwc->interrupts and max_samples_per_tick, then increase
> > hwc->interrupts by 1, but this commit reverses order of these two
> > behaviors, causing the semantics of max_samples_per_tick to change.
> > In literal sense of "max_samples_per_tick", if hwc->interrupts ==
> > max_samples_per_tick, it should not be throttled, therefore, the judgment
> > condition should be changed to "hwc->interrupts > max_samples_per_tick".
> >
> > In fact, this may cause the hardlockup to fail, The minimum value of
> > max_samples_per_tick may be 1, in this case, the return value of
> > __perf_event_account_interrupt function is 1.
> > As a result, nmi_watchdog gets throttled, which would stop PMU (Use x86
> > architecture as an example, see x86_pmu_handle_irq).
> >
> > Fixes: e050e3f0a71b ("perf: Fix broken interrupt rate throttling")
> > Signed-off-by: Yang Jihong <yangjihong1@xxxxxxxxxx>
> > ---
> >
> > Changes since v2:
> >    - Add fixed commit.
> >
> > Changes since v1:
> >    - Modify commit title.
> >
> >   kernel/events/core.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/kernel/events/core.c b/kernel/events/core.c
> > index f79fd8b87f75..0540a8653906 100644
> > --- a/kernel/events/core.c
> > +++ b/kernel/events/core.c
> > @@ -9434,7 +9434,7 @@ __perf_event_account_interrupt(struct perf_event 
> > *event, int throttle)
> >       } else {
> >           hwc->interrupts++;
> >           if (unlikely(throttle
> > -                 && hwc->interrupts >= max_samples_per_tick)) {
> > +                 && hwc->interrupts > max_samples_per_tick)) {
> >               __this_cpu_inc(perf_throttled_count);
> >               tick_dep_set_cpu(smp_processor_id(), 
> > TICK_DEP_BIT_PERF_EVENTS);
> >               hwc->interrupts = MAX_INTERRUPTS;
>
> .