[PATCH v2 tip/core/rcu 07/10] ipc: Replace spin_unlock_wait() with lock/unlock pair

["Paul E. McKenney" <paulmck@linux.vnet.ibm.com>]

There is no agreed-upon definition of spin_unlock_wait()'s semantics,
and it appears that all callers could do just as well with a lock/unlock
pair.  This commit therefore replaces the spin_unlock_wait() call in
exit_sem() with spin_lock() followed immediately by spin_unlock().
This should be safe from a performance perspective because exit_sem()
is rarely invoked in production.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Alan Stern <stern@rowland.harvard.edu>
Cc: Andrea Parri <parri.andrea@gmail.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Acked-by: Manfred Spraul <manfred@colorfullife.com>
---
 ipc/sem.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/ipc/sem.c b/ipc/sem.c
index 9e70cd7a17da..2570830e29fc 100644
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -2091,7 +2091,8 @@ void exit_sem(struct task_struct *tsk)
 			 * possibility where we exit while freeary() didn't
 			 * finish unlocking sem_undo_list.
 			 */
-			spin_unlock_wait(&ulp->lock);
+			spin_lock(&ulp->lock);
+			spin_unlock(&ulp->lock);
 			rcu_read_unlock();
 			break;
 		}
-- 
2.5.2