From: Mike Frysinger <vapier@gentoo.org>
To: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Russell King <linux@arm.linux.org.uk>,
Benjamin Herrenschmidt <benh@kernel.crashing.org>,
Richard Weinberger <richard@nod.at>,
Paul Mundt <lethal@linux-sh.org>,
Peter Zijlstra <a.p.zijlstra@chello.nl>,
KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>,
John Stultz <john.stultz@linaro.org>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org,
uclinux-dist-devel@blackfin.uclinux.org,
linuxppc-dev@lists.ozlabs.org, linux-sh@vger.kernel.org,
user-mode-linux-devel@lists.sourceforge.net,
linaro-kernel@lists.linaro.org, patches@linaro.org,
linux-mm@kvack.org
Subject: Re: [PATCH 5/9] blackfin: A couple of task->mm handling fixes
Date: Fri, 1 Jun 2012 00:36:35 -0400 [thread overview]
Message-ID: <201206010036.40468.vapier@gentoo.org> (raw)
In-Reply-To: <20120423070901.GE30752@lizard>
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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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next prev parent reply other threads:[~2012-06-01 4:36 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-04-23 7:06 [PATCH v3 0/9] Fixes for common mistakes w/ for_each_process and task->mm Anton Vorontsov
2012-04-23 7:07 ` [PATCH 1/9] cpu: Introduce clear_tasks_mm_cpumask() helper Anton Vorontsov
2012-04-26 23:59 ` Andrew Morton
2012-05-01 10:45 ` Peter Zijlstra
2012-05-05 1:47 ` [PATCH] cpu: Document clear_tasks_mm_cpumask() Anton Vorontsov
2012-05-05 1:47 ` [PATCH 1/9] cpu: Introduce clear_tasks_mm_cpumask() helper Anton Vorontsov
2012-04-23 7:08 ` [PATCH 2/9] arm: Use clear_tasks_mm_cpumask() Anton Vorontsov
2012-04-23 7:08 ` [PATCH 3/9] powerpc: " Anton Vorontsov
2012-04-23 7:08 ` [PATCH 4/9] sh: " Anton Vorontsov
2012-04-23 7:09 ` [PATCH 5/9] blackfin: A couple of task->mm handling fixes Anton Vorontsov
2012-06-01 4:36 ` Mike Frysinger [this message]
2012-04-23 7:09 ` [PATCH 6/9] blackfin: Fix possible deadlock in decode_address() Anton Vorontsov
2012-04-23 7:09 ` [PATCH 7/9] um: Should hold tasklist_lock while traversing processes Anton Vorontsov
2012-04-23 14:57 ` Richard Weinberger
2012-04-23 15:40 ` Anton Vorontsov
2012-04-23 7:09 ` [PATCH 8/9] um: Fix possible race on task->mm Anton Vorontsov
2012-04-23 7:09 ` [PATCH 9/9] um: Properly check all process' threads for a live mm Anton Vorontsov
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