linux-kernel - Re: [tip:perf/core] perf: Fix PERF_EVENT_IOC

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Date:	Wed, 12 Aug 2015 19:07:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vincent.weaver@...ne.edu>
Cc:	mingo@...nel.org, tglx@...utronix.de, linux-kernel@...r.kernel.org,
	hpa@...or.com, torvalds@...ux-foundation.org,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:perf/core] perf: Fix PERF_EVENT_IOC_PERIOD migration race

On Wed, Aug 12, 2015 at 09:49:40AM -0400, Vince Weaver wrote:
> On Wed, 12 Aug 2015, tip-bot for Peter Zijlstra wrote:
> 
> > Commit-ID:  c7999c6f3fed9e383d3131474588f282ae6d56b9
> > Gitweb:     http://git.kernel.org/tip/c7999c6f3fed9e383d3131474588f282ae6d56b9
> > Author:     Peter Zijlstra <peterz@...radead.org>
> > AuthorDate: Tue, 4 Aug 2015 19:22:49 +0200
> > Committer:  Ingo Molnar <mingo@...nel.org>
> > CommitDate: Wed, 12 Aug 2015 11:37:22 +0200
> > 
> > perf: Fix PERF_EVENT_IOC_PERIOD migration race
> > 
> > I ran the perf fuzzer, which triggered some WARN()s which are due to
> > trying to stop/restart an event on the wrong CPU.
> 
> Do you have a list of which WARNs this should fix?  Just so I can 
> update my bug tracker.

I think this triggered:

arch/x86/kernel/cpu/perf_event.c:x86_pmu_del()

	if (WARN_ON_ONCE(i == cpuc->n_events)) /* called ->del() without ->add() ? */


Through perf_ioctl()->perf_event_period().

I didn't safe a copy of the exact backtrace.
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