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    Subject[PATCH 4.13 095/110] md: fix a race condition for flush request handling
    Date
    4.13-stable review patch.  If anyone has any objections, please let me know.

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

    From: Shaohua Li <shli@fb.com>

    commit 79bf31a3b2a7ca467cfec8ff97d359a77065d01f upstream.

    md_submit_flush_data calls pers->make_request, which missed the suspend check.
    Fix it with the new md_handle_request API.

    Reported-by: Nate Dailey <nate.dailey@stratus.com>
    Tested-by: Nate Dailey <nate.dailey@stratus.com>
    Fix: cc27b0c78c79(md: fix deadlock between mddev_suspend() and md_write_start())
    Reviewed-by: NeilBrown <neilb@suse.com>
    Signed-off-by: Shaohua Li <shli@fb.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    drivers/md/md.c | 14 ++++++++++----
    1 file changed, 10 insertions(+), 4 deletions(-)

    --- a/drivers/md/md.c
    +++ b/drivers/md/md.c
    @@ -439,16 +439,22 @@ static void md_submit_flush_data(struct
    struct mddev *mddev = container_of(ws, struct mddev, flush_work);
    struct bio *bio = mddev->flush_bio;

    + /*
    + * must reset flush_bio before calling into md_handle_request to avoid a
    + * deadlock, because other bios passed md_handle_request suspend check
    + * could wait for this and below md_handle_request could wait for those
    + * bios because of suspend check
    + */
    + mddev->flush_bio = NULL;
    + wake_up(&mddev->sb_wait);
    +
    if (bio->bi_iter.bi_size == 0)
    /* an empty barrier - all done */
    bio_endio(bio);
    else {
    bio->bi_opf &= ~REQ_PREFLUSH;
    - mddev->pers->make_request(mddev, bio);
    + md_handle_request(mddev, bio);
    }
    -
    - mddev->flush_bio = NULL;
    - wake_up(&mddev->sb_wait);
    }

    void md_flush_request(struct mddev *mddev, struct bio *bio)

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