From: Andrea Parri <andrea.parri@amarulasolutions.com>
Date: Mon, 20 May 2019 17:23:56 +0000 (+0200)
Subject: bio: fix improper use of smp_mb__before_atomic()
X-Git-Tag: v5.2-rc2~8^2~9
X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=f381c6a4bd0ae0fde2d6340f1b9bb0f58d915de6;p=linux.git

bio: fix improper use of smp_mb__before_atomic()

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@vger.kernel.org
Reported-by: "Paul E. McKenney" <paulmck@linux.ibm.com>
Reported-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Andrea Parri <andrea.parri@amarulasolutions.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: linux-block@vger.kernel.org
Cc: "Paul E. McKenney" <paulmck@linux.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---

diff --git a/include/linux/bio.h b/include/linux/bio.h
index ea73df36529a..0f23b5682640 100644
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -210,7 +210,7 @@ static inline void bio_cnt_set(struct bio *bio, unsigned int count)
 {
 	if (count != 1) {
 		bio->bi_flags |= (1 << BIO_REFFED);
-		smp_mb__before_atomic();
+		smp_mb();
 	}
 	atomic_set(&bio->__bi_cnt, count);
 }