From: Frederic Weisbecker <fweisbec@gmail.com>
Date: Fri, 11 Oct 2013 15:41:11 +0000 (+0200)
Subject: posix-timers: Use sighand lock instead of tasklist_lock for task clock sample
X-Git-Tag: v3.14-rc1~169^2~4^2~3
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=50875788a1d4a3f662a27ed13cd05282d835939a;p=pandora-kernel.git

posix-timers: Use sighand lock instead of tasklist_lock for task clock sample

There is no need for the tasklist_lock just to take a process
wide clock sample.

All we need is to get a coherent sample that doesn't race with
exit() and exec():

* exit() may be concurrently reaping a task and flushing its time

* sighand is unstable under exit() and exec(), and the latter also
  result in group leader that can change

To protect against these, locking the target's sighand is enough.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Kosaki Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---

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