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>

1 files changed, 2 insertions, 13 deletions

diff --git a/fs/exec.c b/fs/exec.c
index a13883903ee9..8fccc276d40d 100644
--- 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.