On Thu, May 21, 2015 at 06:07:20AM -0700, Stephane Eranian wrote: > On Thu, May 21, 2015 at 5:56 AM, Peter Zijlstra <[email protected]> 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?
That's a read. The <context switch> can include a call to x86_schedule_events(). > 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? No, but x86_schedule_event() can modify event state, which is the fail. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
