[PATCH] pi-futex: fix mm_struct memory leak

lock_queue was getting called essentially twice in a row and was
continually incrementing the mm_count ref count, thus causing a memory
leak.

Dinakar Guniguntala provided a proper fix for the problem that simply grabs
the spinlock for the hash bucket queue rather than calling lock_queue.

The second time we do a queue_lock in futex_lock_pi, we really only need to
take the hash bucket lock.

Signed-off-by: Dinakar Guniguntala <dino@in.ibm.com>
Signed-off-by: Vernon Mauery <vernux@us.ibm.com>
Acked-by: Paul E. McKenney <paulmck@us.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/futex.c

@@ -1208,7 +1208,7 @@ static int do_futex_lock_pi(u32 __user *uaddr, int detect, int trylock,
 	}
 
 	down_read(&curr->mm->mmap_sem);
-	hb = queue_lock(&q, -1, NULL);
+	spin_lock(q.lock_ptr);
 
 	/*
 	 * Got the lock. We might not be the anticipated owner if we