linux-kernel - Re: [PATCH 1/2] oprofile: fix race condition in event

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Date:	Mon, 12 Oct 2009 23:28:11 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Robert Richter <robert.richter@....com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	oprofile-list <oprofile-list@...ts.sourceforge.net>,
	David Rientjes <rientjes@...gle.com>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 1/2] oprofile: fix race condition in event_buffer free


* Robert Richter <robert.richter@....com> wrote:

> On 09.10.09 21:33:29, Robert Richter wrote:
> > From: David Rientjes <rientjes@...gle.com>
> > 
> > Looking at the 2.6.31-rc9 code, it appears there is a race condition
> > in the event_buffer cleanup code path (shutdown). This could lead to
> > kernel panic as some CPUs may be operating on the event buffer AFTER
> > it has been freed. The attached patch solves the problem and makes
> > sure CPUs check if the buffer is not NULL before they access it as
> > some may have been spinning on the mutex while the buffer was being
> > freed.
> > 
> > The race may happen if the buffer is freed during pending reads. But
> > it is not clear why there are races in add_event_entry() since all
> > workqueues or handlers are canceled or flushed before the event buffer
> > is freed.
> > 
> > Signed-off-by: David Rientjes <rientjes@...gle.com>
> > Signed-off-by: Stephane Eranian <eranian@...gle.com>
> > Signed-off-by: Robert Richter <robert.richter@....com>
> 
> Ingo,
> 
> you can also pull the patches from here:
> 
>  git://git.kernel.org/pub/scm/linux/kernel/git/rric/oprofile.git urgent
> 
> Thanks.

Pulled, thanks Robert!

	Ingo
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