[PATCH 4.14 005/193] bio: fix improper use of smp_mb__before_atomic()

[Greg Kroah-Hartman]

From: Andrea Parri <andrea.pa...@amarulasolutions.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: sta...@vger.kernel.org
Reported-by: "Paul E. McKenney" <paul...@linux.ibm.com>
Reported-by: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Andrea Parri <andrea.pa...@amarulasolutions.com>
Reviewed-by: Ming Lei <ming....@redhat.com>
Cc: Jens Axboe <ax...@kernel.dk>
Cc: Ming Lei <ming....@redhat.com>
Cc: linux-bl...@vger.kernel.org
Cc: "Paul E. McKenney" <paul...@linux.ibm.com>
Cc: Peter Zijlstra <pet...@infradead.org>
Signed-off-by: Jens Axboe <ax...@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -260,7 +260,7 @@ 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);
 }