linux-kernel - Re: [PATCH v2] perf/core: fix a possible deadlock scenario

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Date:   Mon, 23 Jul 2018 18:44:43 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v2] perf/core: fix a possible deadlock scenario

On Mon, Jul 23, 2018 at 6:35 PM Cong Wang <xiyou.wangcong@...il.com> wrote:
>
> Hi, Peter, Andi
>
> While reviewing the deadlock, I find out it looks like we could have the
> following infinite recursion too:
>
> perf_event_account_interrupt()
> __perf_event_account_interrupt()
> perf_adjust_period()
> event->pmu->stop
> x86_pmu_stop()
> x86_pmu.disable()

Hmm, x86_pmu_stop() calls __test_and_clear_bit(), so
we should not call x86_pmu.disable() twice here.



> intel_pmu_disable_event()
> intel_pmu_pebs_disable()
> intel_pmu_drain_pebs_buffer()
> intel_pmu_drain_pebs_nhm()
> <repeat....>
>
> This time is pure hardware events, attr.freq must be non-zero.
>
> And, we could enter this infinite recursion in NMI handler too:
>
> intel_pmu_handle_irq()
> perf_event_overflow()
> __perf_event_overflow()
> __perf_event_account_interrupt()
> ....
>
> Or this is impossible too?
>
> Thanks!