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    Subject[PATCH 51/88] md: protect against crash upon fsync on ro array
    Date
    3.5.7.8 -stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Sebastian Riemer <sebastian.riemer@profitbricks.com>

    commit bbfa57c0f2243a7c31fd248d22e9861a2802cad5 upstream.

    If an fsync occurs on a read-only array, we need to send a
    completion for the IO and may not increment the active IO count.
    Otherwise, we hit a bug trace and can't stop the MD array anymore.

    By advice of Christoph Hellwig we return success upon a flush
    request but we return -EROFS for other writes.
    We detect flush requests by checking if the bio has zero sectors.

    This patch is suitable to any -stable kernel to which it applies.

    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Ben Hutchings <ben@decadent.org.uk>
    Cc: NeilBrown <neilb@suse.de>
    Signed-off-by: Sebastian Riemer <sebastian.riemer@profitbricks.com>
    Reported-by: Ben Hutchings <ben@decadent.org.uk>
    Acked-by: Paul Menzel <paulepanter@users.sourceforge.net>
    Signed-off-by: NeilBrown <neilb@suse.de>
    Signed-off-by: Luis Henriques <luis.henriques@canonical.com>
    ---
    drivers/md/md.c | 4 ++++
    1 file changed, 4 insertions(+)

    diff --git a/drivers/md/md.c b/drivers/md/md.c
    index 97edf9e..b7a551d 100644
    --- a/drivers/md/md.c
    +++ b/drivers/md/md.c
    @@ -344,6 +344,10 @@ static void md_make_request(struct request_queue *q, struct bio *bio)
    bio_io_error(bio);
    return;
    }
    + if (mddev->ro == 1 && unlikely(rw == WRITE)) {
    + bio_endio(bio, bio_sectors(bio) == 0 ? 0 : -EROFS);
    + return;
    + }
    smp_rmb(); /* Ensure implications of 'active' are visible */
    rcu_read_lock();
    if (mddev->suspended) {
    --
    1.8.1.2


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