linux-kernel - [PATCH] kernel/futex: Fix barrier comment

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Message-Id: <20190206185602.949-1-dave@stgolabs.net>
Date:   Wed,  6 Feb 2019 10:56:02 -0800
From:   Davidlohr Bueso <dave@...olabs.net>
To:     mingo@...nel.org, tglx@...utronix.de
Cc:     peterz@...radead.org, linux-kernel@...r.kernel.org,
        dave@...olabs.net, Davidlohr Bueso <dbueso@...e.de>
Subject: [PATCH] kernel/futex: Fix barrier comment

The current comment for the barrier that guarantees that waiter
increment is always before taking the hb spinlock (barrier (A))
needs to be fixed. We are obviously referring to hb_waiters_inc,
which is a full barrier.

Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Davidlohr Bueso <dbueso@...e.de>
---
 kernel/futex.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/futex.c b/kernel/futex.c
index fdd312da0992..5ec2473a3497 100644
--- 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;
 }
 
-- 
2.16.4