Commit dfcce791 authored Apr 16, 2015 by Kirill Tkhai Committed by Linus Torvalds Apr 17, 2015

fs/exec.c:de_thread: move notify_count write under lock



We set sig->notify_count = -1 between RELEASE and ACQUIRE operations:

	spin_unlock_irq(lock);
	...
	if (!thread_group_leader(tsk)) {
		...
                for (;;) {
			sig->notify_count = -1;
                        write_lock_irq(&tasklist_lock);

There are no restriction on it so other processors may see this STORE
mixed with other STOREs in both areas limited by the spinlocks.

Probably, it may be reordered with the above

	sig->group_exit_task = tsk;
	sig->notify_count = zap_other_threads(tsk);

in some way.

Set it under tasklist_lock locked to be sure nothing will be reordered.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 6e399cd1

fs/exec.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -926,10 +926,14 @@ static int de_thread(struct task_struct *tsk)
		if (!thread_group_leader(tsk)) {
		struct task_struct *leader = tsk->group_leader;

		sig->notify_count = -1; /* for exit_notify() */
		for (;;) {
		threadgroup_change_begin(tsk);
		write_lock_irq(&tasklist_lock);
		/*
		* Do this under tasklist_lock to ensure that
		* exit_notify() can't miss ->group_exit_task
		*/
		sig->notify_count = -1;
		if (likely(leader->exit_state))
		break;
		__set_current_state(TASK_KILLABLE);

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