posix-timers: simplify de_thread()->exit_itimers() path

Impact: simplify code

de_thread() postpones release_task(leader) until after exit_itimers().
This was needed because !SIGEV_THREAD_ID timers could use ->group_leader
without get_task_struct(). With the recent changes we can release the
leader earlier and simplify the code.
Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

fs/exec.c

@@ -772,7 +772,6 @@ 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;
-	struct task_struct *leader = NULL;
 	int count;
 
 	if (thread_group_empty(tsk))
@@ -810,7 +809,7 @@ static int de_thread(struct task_struct *tsk)
 	 * and to assume its PID:
 	 */
 	if (!thread_group_leader(tsk)) {
-		leader = tsk->group_leader;
+		struct task_struct *leader = tsk->group_leader;
 
 		sig->notify_count = -1;	/* for exit_notify() */
 		for (;;) {
@@ -862,8 +861,9 @@ static int de_thread(struct task_struct *tsk)
 
 		BUG_ON(leader->exit_state != EXIT_ZOMBIE);
 		leader->exit_state = EXIT_DEAD;
-
 		write_unlock_irq(&tasklist_lock);
+
+		release_task(leader);
 	}
 
 	sig->group_exit_task = NULL;
@@ -872,8 +872,6 @@ static int de_thread(struct task_struct *tsk)
 no_thread_group:
 	exit_itimers(sig);
 	flush_itimer_signals();
-	if (leader)
-		release_task(leader);
 
 	if (atomic_read(&oldsighand->count) != 1) {
 		struct sighand_struct *newsighand;