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From: Peter Zijlstra <>
To: Kees Cook <>
Cc:, Ingo Molnar <>,
	Arnaldo Carvalho de Melo <>,
	Alexander Shishkin <>,
	John Dias <>, Min Chong <>
Subject: Re: [PATCH] perf: protect group_leader from races that cause ctx
Date: Fri, 6 Jan 2017 10:32:51 +0100	[thread overview]
Message-ID: <20170106093251.GL3093@worktop> (raw)
In-Reply-To: <20170105231429.GA83592@beast>

On Thu, Jan 05, 2017 at 03:14:29PM -0800, Kees Cook wrote:
> From: John Dias <>
> When moving a group_leader perf event from a software-context to
> a hardware-context, there's a race in checking and updating that
> context. The existing locking solution doesn't work; note that it tries
> to grab a lock inside the group_leader's context object, which you can
> only get at by going through a pointer that should be protected from these
> races. If two threads trigger this operation simultaneously, the refcount
> of 'perf_event_context' will fall to zero and the object may be freed.
> To avoid that problem, and to produce a simple solution, we can just
> use a lock per group_leader to protect all checks on the group_leader's
> context. The new lock is grabbed and released when no context locks are
> held.

This Changelog really stinks. I'll go try and reverse engineer the thing

  reply	other threads:[~2017-01-06  9:36 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-01-05 23:14 Kees Cook
2017-01-06  9:32 ` Peter Zijlstra [this message]
2017-01-06 13:14   ` Peter Zijlstra
2017-01-06 20:39     ` Kees Cook
2017-01-07 16:29       ` John Dias
2017-01-09 23:16         ` Kees Cook
2017-01-10  8:46       ` Peter Zijlstra
2017-01-10 10:16       ` Ingo Molnar
2017-01-10 23:54         ` Kees Cook
2017-01-14 12:28     ` [tip:perf/urgent] perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race tip-bot for Peter Zijlstra

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