linux-kernel - [PATCH 4.19 006/276] bio: fix improper use of smp_mb__before

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Message-Id: <20190530030523.764119003@linuxfoundation.org>
Date:   Wed, 29 May 2019 20:02:44 -0700
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, "Paul E. McKenney" <paulmck@...ux.ibm.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrea Parri <andrea.parri@...rulasolutions.com>,
        Ming Lei <ming.lei@...hat.com>, Jens Axboe <axboe@...nel.dk>,
        linux-block@...r.kernel.org
Subject: [PATCH 4.19 006/276] bio: fix improper use of smp_mb__before_atomic()

From: Andrea Parri <andrea.parri@...rulasolutions.com>

commit f381c6a4bd0ae0fde2d6340f1b9bb0f58d915de6 upstream.

This barrier only applies to the read-modify-write operations; in
particular, it does not apply to the atomic_set() primitive.

Replace the barrier with an smp_mb().

Fixes: dac56212e8127 ("bio: skip atomic inc/dec of ->bi_cnt for most use cases")
Cc: stable@...r.kernel.org
Reported-by: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Reported-by: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Andrea Parri <andrea.parri@...rulasolutions.com>
Reviewed-by: Ming Lei <ming.lei@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>
Cc: Ming Lei <ming.lei@...hat.com>
Cc: linux-block@...r.kernel.org
Cc: "Paul E. McKenney" <paulmck@...ux.ibm.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Signed-off-by: Jens Axboe <axboe@...nel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 include/linux/bio.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -257,7 +257,7 @@ static inline void bio_cnt_set(struct bi
 {
 	if (count != 1) {
 		bio->bi_flags |= (1 << BIO_REFFED);
-		smp_mb__before_atomic();
+		smp_mb();
 	}
 	atomic_set(&bio->__bi_cnt, count);
 }