signals: send_group_sigqueue: don't take tasklist_lock

handle_stop_signal() was changed, now send_group_sigqueue() doesn't need
tasklist_lock.

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Roland McGrath <roland@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/signal.c

@@ -1335,7 +1335,6 @@ send_group_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
 
 	BUG_ON(!(q->flags & SIGQUEUE_PREALLOC));
 
-	read_lock(&tasklist_lock);
 	/* Since it_lock is held, p->sighand cannot be NULL. */
 	spin_lock_irqsave(&p->sighand->siglock, flags);
 
@@ -1344,7 +1343,7 @@ send_group_sigqueue(int sig, struct sigqueue *q, struct task_struct *p)
 	__group_complete_signal(sig, p);
 
 	spin_unlock_irqrestore(&p->sighand->siglock, flags);
-	read_unlock(&tasklist_lock);
+
 	return ret;
 }