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    Subject[PATCH 4.14 005/193] bio: fix improper use of smp_mb__before_atomic()
    Date
    From: Andrea Parri <andrea.parri@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: 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>

    ---
    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);
    }

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