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.wangc...@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. 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/20170928121823.430053...@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. 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?