From: Anton Vorontsov <anton.vorontsov@linaro.org>
Date: Thu, 31 May 2012 23:26:25 +0000 (-0700)
Subject: um: fix possible race on task->mm
X-Git-Tag: v3.5-rc1~21^2~30
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=137d1a26c842a384c98dd2a6a605014fddf5c777;p=pandora-kernel.git

um: fix possible race on task->mm

Checking for task->mm is dangerous as ->mm might disappear (exit_mm()
assigns NULL under task_lock(), so tasklist lock is not enough).

We can't use get_task_mm()/mmput() pair as mmput() might sleep, so let's
take the task lock while we care about its mm.

Note that we should also use find_lock_task_mm() to check all process'
threads for a valid mm, but for uml we'll do it in a separate patch.

Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
Cc: Richard Weinberger <richard@nod.at>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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