futex: Fix barrier comment

Davidlohr Bueso · KAGA-KOKO · commit 6f568ebe2afe · 2019-02-08T13:00:35.000+01:00
The current comment for the barrier that guarantees that waiter increment is always before taking the hb spinlock (barrier (A)) needs to be fixed as it is misplaced. This is obviously referring to hb_waiters_inc, which is a full barrier. Reported-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Davidlohr Bueso <dbueso@suse.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lkml.kernel.org/r/20190206185602.949-1-dave@stgolabs.net
diff --git a/kernel/futex.c b/kernel/futex.c
@@ -2221,11 +2221,11 @@ static inline struct futex_hash_bucket *queue_lock(struct futex_q *q)
 	 * decrement the counter at queue_unlock() when some error has
 	 * occurred and we don't end up adding the task to the list.
 	 */
-	hb_waiters_inc(hb);
+	hb_waiters_inc(hb); /* implies smp_mb(); (A) */
 
 	q->lock_ptr = &hb->lock;
 
-	spin_lock(&hb->lock); /* implies smp_mb(); (A) */
+	spin_lock(&hb->lock);
 	return hb;
 }
 
