Subject: Re: Exiting with locks still held (was Re: [PATCH] kmemleak: Fix 
	scheduling-while-atomic bug)
From: Catalin Marinas <catalin.marinas@arm.com>
To: Pekka Enberg <penberg@cs.helsinki.fi>
Cc: Ingo Molnar <mingo@elte.hu>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       git-commits-head@vger.kernel.org
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Organization: ARM Ltd
Date: Thu, 02 Jul 2009 14:06:03 +0100
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On Thu, 2009-07-02 at 15:54 +0300, Pekka Enberg wrote:
> On Thu, Jul 2, 2009 at 3:48 PM, Catalin Marinas<catalin.marinas@arm.com> wrote:
> > It could be but I can't figure out a solution. If there is only one task
> > opening and closing the kmemleak file, everything is fine. In
> > combination with shell piping I think I get the kmemleak file descriptor
> > released from a different task than the one that opened it.
> >
> > For example, the badly written code below opens kmemleak and acquires
> > the scan_mutex in the parent task but releases it in the child (it needs
> > a few tries to trigger it). With waitpid() in parent everything is fine.
[...]
> Well, you are not supposed to hold on to locks when returning from a
> system call ("sys_open") anyway. You can probably do the exclusion
> with a kmemcheck specific flag?

Acquiring the mutex in "open" and releasing it in "release" was easier.
I'll see if I can move the mutex to the seq_read functions which
actually need it.

-- 
Catalin

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