signals: de_thread: simplify the ->child_reaper switching

Now that we rely on SIGNAL_UNKILLABLE flag, de_thread() doesn't need the nasty
hack to kill the old ->child_reaper during the mt-exec.

This also means we can avoid taking tasklist_lock around zap_other_threads().

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>

diff --git a/fs/exec.c b/fs/exec.c
index a138839..8fccc27 100644 (file)
--- a/fs/exec.c
+++ b/fs/exec.c
@@ -766,9 +766,7 @@ static int de_thread(struct task_struct *tsk)
 
        /*
         * Kill all other threads in the thread group.
-        * We must hold tasklist_lock to call zap_other_threads.
         */
-       read_lock(&tasklist_lock);
        spin_lock_irq(lock);
        if (signal_group_exit(sig)) {
                /*
@@ -776,21 +774,10 @@ static int de_thread(struct task_struct *tsk)
                 * return so that the signal is processed.
                 */
                spin_unlock_irq(lock);
-               read_unlock(&tasklist_lock);
                return -EAGAIN;
        }
-
-       /*
-        * child_reaper ignores SIGKILL, change it now.
-        * Reparenting needs write_lock on tasklist_lock,
-        * so it is safe to do it under read_lock.
-        */
-       if (unlikely(tsk->group_leader == task_child_reaper(tsk)))
-               task_active_pid_ns(tsk)->child_reaper = tsk;
-
        sig->group_exit_task = tsk;
        zap_other_threads(tsk);
-       read_unlock(&tasklist_lock);
 
        /* Account for the thread group leader hanging around: */
        count = thread_group_leader(tsk) ? 1 : 2;
@@ -821,6 +808,8 @@ static int de_thread(struct task_struct *tsk)
                        schedule();
                }
 
+               if (unlikely(task_child_reaper(tsk) == leader))
+                       task_active_pid_ns(tsk)->child_reaper = tsk;
                /*
                 * The only record we have of the real-time age of a
                 * process, regardless of execs it's done, is start_time.