Messages in this thread | | | From | Cong Wang <> | Date | Wed, 25 Jul 2018 11:44:34 -0700 | Subject | Re: [PATCH v2] perf/core: fix a possible deadlock scenario |
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On Tue, Jul 24, 2018 at 2:18 AM Peter Zijlstra <peterz@infradead.org> wrote: > > On Mon, Jul 23, 2018 at 06:44:43PM -0700, Cong Wang wrote: > > On Mon, Jul 23, 2018 at 6:35 PM Cong Wang <xiyou.wangcong@gmail.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. > > Right, but since we set HES_UPTODATE after calling > x86_perf_event_update() that can in fact recurse.
I don't see how HES_UPTODATE flag or x86_perf_event_update() could affect the path on this call chain.
> > Now, I don't think that'll be fatal, but it might be good to test that. > > If you pick these patches: > > https://lkml.kernel.org/r/20170928121823.430053219@infradead.org > > use force_early_printk (and actually configure a serial early_printk) > and put a printk() in x86_pmu_stop() and then run the perf_fuzzer or > something to try and reproduce.
Is this patchset to make printk() working in NMI context? But printk() is already used in NMI context, see perf_event_print_debug() which is called in intel_pmu_handle_irq().
> > But paranoia suggets moving that HES_UPTODATE thing one line up. > > > > 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? > > I'm not sure I see this second one.. can you be a little more specific?
In fact, it is this:
intel_pmu_handle_irq() x86_pmu.drain_pebs() intel_pmu_drain_pebs_nhm() perf_event_account_interrupt() __perf_event_account_interrupt() perf_adjust_period() event->pmu->stop() x86_pmu_stop() x86_pmu.disable() intel_pmu_disable_event() intel_pmu_pebs_disable() intel_pmu_drain_pebs_buffer() <repeat....>
Thanks!
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