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Subject[PATCH] de_thread: Move notify_count write under lock
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The write operation may be reordered with the setting of group_exit_task.
If so, this fires in exit_notify().

Looks like, it's not good to add smp barriers for this case, especially
in exit_notify(), so let's put the notify_count write under write lock.

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
---
fs/exec.c | 8 +++++++-
1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/fs/exec.c b/fs/exec.c
index ad8798e..42782d5 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -920,10 +920,16 @@ 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);
+ /*
+ * We could set it once outside the for() cycle, but
+ * this requires to use SMP barriers there and in
+ * exit_notify(), because the write operation may
+ * be reordered with the setting of group_exit_task.
+ */
+ sig->notify_count = -1; /* for exit_notify() */
if (likely(leader->exit_state))
break;
__set_current_state(TASK_KILLABLE);




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