From: Oleg Nesterov <oleg@redhat.com>
Date: Tue, 30 Apr 2013 22:28:20 +0000 (-0700)
Subject: exec: do not abuse ->cred_guard_mutex in threadgroup_lock()
X-Git-Tag: omap-for-v3.10/dt-fixes-for-merge-window~88^2~35
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=e56fb2874015370e3b7f8d85051f6dce26051df9;p=pandora-kernel.git

exec: do not abuse ->cred_guard_mutex in threadgroup_lock()

threadgroup_lock() takes signal->cred_guard_mutex to ensure that
thread_group_leader() is stable.  This doesn't look nice, the scope of
this lock in do_execve() is huge.

And as Dave pointed out this can lead to deadlock, we have the
following dependencies:

	do_execve:		cred_guard_mutex -> i_mutex
	cgroup_mount:		i_mutex -> cgroup_mutex
	attach_task_by_pid:	cgroup_mutex -> cred_guard_mutex

Change de_thread() to take threadgroup_change_begin() around the
switch-the-leader code and change threadgroup_lock() to avoid
->cred_guard_mutex.

Note that de_thread() can't sleep with ->group_rwsem held, this can
obviously deadlock with the exiting leader if the writer is active, so it
does threadgroup_change_end() before schedule().

Reported-by: Dave Jones <davej@redhat.com>
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
---

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