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>

diff --git a/fs/exec.c b/fs/exec.c
index a5fef835ebc59fe1dab0311dab0f4fe427894b50..02bfd980a40c7df568bc1f9b847600fd76c2861d 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -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);