bio: fix improper use of smp_mb__before_atomic()

BugLink: https://bugs.launchpad.net/bugs/1838700
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@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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

diff --git a/include/linux/bio.h b/include/linux/bio.h
index 3440870712d4a77a5e4a031ac52101cf811476d2..9ec7626a250db5487c1d215752091124e40fd8a6 100644 (file)
--- a/include/linux/bio.h
+++ b/include/linux/bio.h
@@ -253,7 +253,7 @@ 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);
 }