exit: wait: drop tasklist_lock before psig->c* accounting

wait_task_zombie() no longer needs tasklist_lock to accumulate the
psig->c* counters, we can drop it right after cmpxchg(exit_state).

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Cc: Aaron Tomlin <atomlin@redhat.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Sterling Alexander <stalexan@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, 7 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 457673d65934..6297eb0f5bd2 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1005,6 +1005,11 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
                 EXIT_TRACE : EXIT_DEAD;
         if (cmpxchg(&p->exit_state, EXIT_ZOMBIE, state) != EXIT_ZOMBIE)
                 return 0;
+        /*
+         * We own this thread, nobody else can reap it.
+         */
+        read_unlock(&tasklist_lock);
+        sched_annotate_sleep();
 
         /*
          * Check thread_group_leader() to exclude the traced sub-threads.
@@ -1064,13 +1069,6 @@ static int wait_task_zombie(struct wait_opts *wo, struct task_struct *p)
                 spin_unlock_irq(&current->sighand->siglock);
         }
 
-        /*
-         * Now we are sure this task is interesting, and no other
-         * thread can reap it because we its state == DEAD/TRACE.
-         */
-        read_unlock(&tasklist_lock);
-        sched_annotate_sleep();
-
         retval = wo->wo_rusage
                 ? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
         status = (p->signal->flags & SIGNAL_GROUP_EXIT)