From: Oleg Nesterov <oleg@redhat.com>
Date: Wed, 17 Jun 2009 23:27:42 +0000 (-0700)
Subject: do_wait: fix the theoretical race with stop/trace/cont
X-Git-Tag: v2.6.31-rc1~206
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f95d39d10fe7d47336e65172f52bf64e0096f983;p=pandora-kernel.git

do_wait: fix the theoretical race with stop/trace/cont

do_wait:

	current->state = TASK_INTERRUPTIBLE;

	read_lock(&tasklist_lock);
	... search for the task to reap ...

In theory, the ->state changing can leak into the critical section.  Since
the child can change its status under read_lock(tasklist) in parallel
(finish_stop/ptrace_stop), we can miss the wakeup if __wake_up_parent()
sees us in TASK_RUNNING state.  Add the barrier.

Also, use __set_current_state() to set TASK_RUNNING.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Acked-by: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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