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Date: Tue, 26 May 2015 12:12:37 +0200 From: Peter Zijlstra <peterz@...radead.org> To: Stephane Eranian <eranian@...gle.com> Cc: Ingo Molnar <mingo@...nel.org>, Vince Weaver <vincent.weaver@...ne.edu>, Jiri Olsa <jolsa@...hat.com>, "Liang, Kan" <kan.liang@...el.com>, LKML <linux-kernel@...r.kernel.org>, Andrew Hunter <ahh@...gle.com>, Maria Dimakopoulou <maria.n.dimakopoulou@...il.com> Subject: Re: [PATCH v2 01/11] perf,x86: Fix event/group validation On Tue, May 26, 2015 at 02:24:38AM -0700, Stephane Eranian wrote: > On Fri, May 22, 2015 at 6:40 AM, Peter Zijlstra <peterz@...radead.org> wrote: > > On Fri, May 22, 2015 at 03:29:06PM +0200, Peter Zijlstra wrote: > >> @@ -788,9 +788,9 @@ int x86_schedule_events(struct cpu_hw_ev > >> x86_pmu.start_scheduling(cpuc); > >> > >> for (i = 0, wmin = X86_PMC_IDX_MAX, wmax = 0; i < n; i++) { > >> + cpuc->event_constraint[i] = NULL; > > > > ^^^ that is new, which is esp. important in light of the > > intel_get_event_constraints() hunk below, which would happily continue > > life with a garbage constraint. > > > You've moved the constraint list from event to cpuc. Yet, it is still > an array of pointers > to constraints. So here you are saying, that in the case validate_group() is > preempted and there is a context switch, there is still a risk of > overwriting the > constraint? I don't see how because validate_group() is using a fake_cpuc. > So yes, the cpuc->event_constraint[] array is modified but it is not the same > as the actual cpuc used by non-validate code. Or am I still missing something? > > When using dynamic constraints, we already have constraint storage in cpuc > (to avoid calling kmalloc() in ctxsw context). Thus, I am wondering if it would > not be easier to always use cpuc for constraint storage (no more pointers). No; the problem here is repeated use of the cpuc (the real one). Say one scheduling run installs a constraint pointer for event i. Then event i gets removed and another installed in the same spot. Then the next scheduling run will pick up the old pointer in intel_get_event_constraints() as a base for the new one. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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