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>

diff --git a/kernel/exit.c b/kernel/exit.c
index 457673d659346ed230c1c99f775afed2fa1ed539..6297eb0f5bd289172055e596825b4758e4edc751 100644 (file)
--- 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)