pi-futex: set PF_EXITING without taking ->pi_lock

It is a bit annoying that do_exit() takes ->pi_lock to set PF_EXITING.  All
we need is to synchronize with lookup_pi_state() which saw this task
without PF_EXITING under ->pi_lock.

Change do_exit() to use spin_unlock_wait().

Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/kernel/exit.c b/kernel/exit.c
index 6ca1e4666e9f..3b8dfffd9329 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -931,13 +931,13 @@ fastcall NORET_TYPE void do_exit(long code)
                 schedule();
         }
 
+        tsk->flags |= PF_EXITING;
         /*
          * tsk->flags are checked in the futex code to protect against
          * an exiting task cleaning up the robust pi futexes.
          */
-        spin_lock_irq(&tsk->pi_lock);
-        tsk->flags |= PF_EXITING;
-        spin_unlock_irq(&tsk->pi_lock);
+        smp_mb();
+        spin_unlock_wait(&tsk->pi_lock);
 
         if (unlikely(in_atomic()))
                 printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",