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From: Davidlohr Bueso <dave@stgolabs.net>
To: mingo@kernel.org, tglx@linutronix.de
Cc: peterz@infradead.org, linux-kernel@vger.kernel.org,
	dave@stgolabs.net, Davidlohr Bueso <dbueso@suse.de>
Subject: [PATCH] kernel/futex: Fix barrier comment
Date: Wed,  6 Feb 2019 10:56:02 -0800
Message-ID: <20190206185602.949-1-dave@stgolabs.net> (raw)

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@infradead.org>
Signed-off-by: Davidlohr Bueso <dbueso@suse.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


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Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-02-06 18:56 Davidlohr Bueso [this message]
2019-02-08 12:04 ` [tip:locking/urgent] futex: " tip-bot for Davidlohr Bueso

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