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Message-Id: <201206010036.40468.vapier@gentoo.org>
Date: Fri, 1 Jun 2012 00:36:35 -0400
From: Mike Frysinger <vapier@...too.org>
To: Anton Vorontsov <anton.vorontsov@...aro.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
Oleg Nesterov <oleg@...hat.com>,
Russell King <linux@....linux.org.uk>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Richard Weinberger <richard@....at>,
Paul Mundt <lethal@...ux-sh.org>,
Peter Zijlstra <a.p.zijlstra@...llo.nl>,
KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
John Stultz <john.stultz@...aro.org>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
uclinux-dist-devel@...ckfin.uclinux.org,
linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
user-mode-linux-devel@...ts.sourceforge.net,
linaro-kernel@...ts.linaro.org, patches@...aro.org,
linux-mm@...ck.org
Subject: Re: [PATCH 5/9] blackfin: A couple of task->mm handling fixes
On Monday 23 April 2012 03:09:01 Anton Vorontsov wrote:
> 1. Working with task->mm w/o getting mm or grabing the task lock is
> dangerous as ->mm might disappear (exit_mm() assigns NULL under
> task_lock(), so tasklist lock is not enough).
that isn't a problem for this code as it specifically checks if it's in an
atomic section. if it is, then task->mm can't go away on us.
> We can't use get_task_mm()/mmput() pair as mmput() might sleep,
> so we have to take the task lock while handle its mm.
if we're not in an atomic section, then sleeping is fine.
> 2. Checking for process->mm is not enough because process' main
> thread may exit or detach its mm via use_mm(), but other threads
> may still have a valid mm.
i don't think it matters for this code (per the reasons above).
> To catch this we use find_lock_task_mm(), which walks up all
> threads and returns an appropriate task (with task lock held).
certainly fine for the non-atomic code path. i guess we'll notice in crashes
if it causes a problem in atomic code paths as well.
-mike
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