[PATCH 3/5] exit: wait: drop tasklist_lock before psig->c* accounting

[Oleg Nesterov]

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@xxxxxxxxxx>
---
 kernel/exit.c |   10 ++++------
 1 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/kernel/exit.c b/kernel/exit.c
index 40d53de..e0914eb 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -1003,6 +1003,10 @@ 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);
 
 	/*
 	 * Check thread_group_leader() to exclude the traced sub-threads.
@@ -1062,12 +1066,6 @@ 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);
-
 	retval = wo->wo_rusage
 		? getrusage(p, RUSAGE_BOTH, wo->wo_rusage) : 0;
 	status = (p->signal->flags & SIGNAL_GROUP_EXIT)
-- 
1.5.5.1

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