Messages in this thread | | | Date | Thu, 21 May 2015 06:07:20 -0700 | Subject | Re: [PATCH 01/10] perf,x86: Fix event/group validation | From | Stephane Eranian <> |
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On Thu, May 21, 2015 at 5:56 AM, Peter Zijlstra <peterz@infradead.org> wrote: > On Thu, May 21, 2015 at 05:35:02AM -0700, Stephane Eranian wrote: >> > Commit e979121b1b15 ("perf/x86/intel: Implement cross-HT corruption >> > bug workaround") made the situation much worse by actually setting the >> > event->hw.constraint value to NULL, so when validation and actual >> > scheduling interact we get NULL ptr derefs. >> > >> >> But x86_schedule_events() does reset the hw.constraint for each invocation: >> >> c = x86_pmu.get_event_constraints(cpuc, i, cpuc->event_list[i]); >> hwc->constraint = c; > > Yes, so if you have: > > validate_group() > > hwc->constraint = c; > Ok, you get that because validate_group() invokes x6_schedule_events() but on the fake_cpuc. This on fake_cpuc->event_list[]->hwc.
> <context switch> > > c = hwc->constraint; > > The second c might not be the first. And where does this assignment come from? For actual scheduling, we are using the actual cpuc, not fake_cpuc. Validate_group() does not modify global cpuc state. Or am I missing something?
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