Re: [PATCH v2 01/11] perf,x86: Fix event/group validation

From: Peter Zijlstra <peterz@infradead.org>
To: Stephane Eranian <eranian@google.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Vince Weaver <vincent.weaver@maine.edu>,
	Jiri Olsa <jolsa@redhat.com>, "Liang, Kan" <kan.liang@intel.com>,
	LKML <linux-kernel@vger.kernel.org>,
	Andrew Hunter <ahh@google.com>,
	Maria Dimakopoulou <maria.n.dimakopoulou@gmail.com>
Subject: Re: [PATCH v2 01/11] perf,x86: Fix event/group validation
Date: Tue, 26 May 2015 14:16:19 +0200	[thread overview]
Message-ID: <20150526121619.GN3644@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <CABPqkBQcKLoHCS3=_1cj4-JCTiOzWDc1=vGp85T-nnoAJQd5-Q@mail.gmail.com>

On Tue, May 26, 2015 at 04:46:07AM -0700, Stephane Eranian wrote:
> On Tue, May 26, 2015 at 3:12 AM, Peter Zijlstra <peterz@infradead.org> wrote:
> > 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@infradead.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;
> >> >

> But where is the code that says: skip reinstalling the constraint
> in intel_get_event_constraints() because there is already a (stale)
> one? I don't see where that is.

IIRC the problem was that the copy from c2 into c1:

	if (c1 && (c1->flags & PERF_X86_EVENT_DYNAMIC)) {
		bitmap_copy(c1->idxmsk, c2->idxmsk, X86_PMC_IDX_MAX);
		c1->weight = c2->weight;
		c2 = c1;
	}

is incomplete. For instance, flags is not copied, and some code down the
line might check that and get wrong flags.

I'm not entirely sure I saw misbehaviour, but I figured I'd better close
that hole and rule out this is contributing to fail.