exit: avoid sig->count in de_thread/__exit_signal synchronization

de_thread() and __exit_signal() use signal_struct->count/notify_count for
synchronization.  We can simplify the code and use ->notify_count only.
Instead of comparing these two counters, we can change de_thread() to set
->notify_count = nr_of_sub_threads, then change __exit_signal() to
dec-and-test this counter and notify group_exit_task.

Note that __exit_signal() checks "notify_count > 0" just for symmetry with
exit_notify(), we could just check it is != 0.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Acked-by: Roland McGrath <roland@redhat.com>
Cc: Veaceslav Falico <vfalico@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 6 deletions

diff --git a/fs/exec.c b/fs/exec.c
index 0c72d23ed0e2..e19de6a80339 100644
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -768,7 +768,6 @@ static int de_thread(struct task_struct *tsk)
         struct signal_struct *sig = tsk->signal;
         struct sighand_struct *oldsighand = tsk->sighand;
         spinlock_t *lock = &oldsighand->siglock;
-        int count;
 
         if (thread_group_empty(tsk))
                 goto no_thread_group;
@@ -785,13 +784,13 @@ static int de_thread(struct task_struct *tsk)
                 spin_unlock_irq(lock);
                 return -EAGAIN;
         }
+
         sig->group_exit_task = tsk;
-        zap_other_threads(tsk);
+        sig->notify_count = zap_other_threads(tsk);
+        if (!thread_group_leader(tsk))
+                sig->notify_count--;
 
-        /* Account for the thread group leader hanging around: */
-        count = thread_group_leader(tsk) ? 1 : 2;
-        sig->notify_count = count;
-        while (atomic_read(&sig->count) > count) {
+        while (sig->notify_count) {
                 __set_current_state(TASK_UNINTERRUPTIBLE);
                 spin_unlock_irq(lock);
                 schedule();