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    Subject[PATCH 3/7] block: loop: fix another reread part failure
    Date
    loop_clr_fd() can be run piggyback with lo_release(), and
    under this situation, reread partition may always fail because
    of bd_mutex which has been held in release path.

    This patch detects the situation by the reference count, and
    call blkdev_reread_part_nolock() to avoid acquiring the lock again.

    In the meantime, this patch switches to new kernel APIs
    of blkdev_reread_part() and blkdev_reread_part_nolock().

    [jarod: this is a merger of my original patch, Ming's patch, and some
    reworking for my reworked first patch in the series.]

    CC: Christoph Hellwig <hch@infradead.org>
    CC: Jens Axboe <axboe@kernel.dk>
    CC: Tejun Heo <tj@kernel.org>
    CC: Alexander Viro <viro@zeniv.linux.org.uk>
    CC: Markus Pargmann <mpa@pengutronix.de>
    CC: Stefan Weinhuber <wein@de.ibm.com>
    CC: Stefan Haberland <stefan.haberland@de.ibm.com>
    CC: Sebastian Ott <sebott@linux.vnet.ibm.com>
    CC: Fabian Frederick <fabf@skynet.be>
    CC: Ming Lei <ming.lei@canonical.com>
    CC: David Herrmann <dh.herrmann@gmail.com>
    CC: Mike Galbraith <bitbucket@online.de>
    CC: Andrew Morton <akpm@linux-foundation.org>
    CC: Peter Zijlstra <peterz@infradead.org>
    CC: nbd-general@lists.sourceforge.net
    CC: linux-s390@vger.kernel.org
    Signed-off-by: Jarod Wilson <jarod@redhat.com>
    ---
    drivers/block/loop.c | 28 ++++++++++++++++++++++++----
    1 file changed, 24 insertions(+), 4 deletions(-)

    diff --git a/drivers/block/loop.c b/drivers/block/loop.c
    index 81a6bc1..ab5c678 100644
    --- a/drivers/block/loop.c
    +++ b/drivers/block/loop.c
    @@ -528,6 +528,26 @@ static int loop_flush(struct loop_device *lo)
    return loop_switch(lo, NULL);
    }

    +static void loop_reread_partitions(struct loop_device *lo,
    + struct block_device *bdev)
    +{
    + int rc;
    + bool in_release;
    +
    + mutex_lock(&lo->lo_open_mutex);
    + in_release = lo->lo_refcnt == 0;
    + mutex_unlock(&lo->lo_open_mutex);
    +
    + /* bd_mutex has been held already in release path */
    + if (in_release)
    + rc = __blkdev_reread_part(bdev);
    + else
    + rc = blkdev_reread_part(bdev);
    + if (rc)
    + pr_warn("%s: partition scan of loop%d (%s) failed (rc=%d)\n",
    + __func__, lo->lo_number, lo->lo_file_name, rc);
    +}
    +
    /*
    * loop_change_fd switched the backing store of a loopback device to
    * a new file. This is useful for operating system installers to free up
    @@ -576,7 +596,7 @@ static int loop_change_fd(struct loop_device *lo, struct block_device *bdev,

    fput(old_file);
    if (lo->lo_flags & LO_FLAGS_PARTSCAN)
    - ioctl_by_bdev(bdev, BLKRRPART, 0);
    + loop_reread_partitions(lo, bdev);
    return 0;

    out_putf:
    @@ -807,7 +827,7 @@ static int loop_set_fd(struct loop_device *lo, fmode_t mode,
    if (part_shift)
    lo->lo_flags |= LO_FLAGS_PARTSCAN;
    if (lo->lo_flags & LO_FLAGS_PARTSCAN)
    - ioctl_by_bdev(bdev, BLKRRPART, 0);
    + loop_reread_partitions(lo, bdev);

    /* Grab the block_device to prevent its destruction after we
    * put /dev/loopXX inode. Later in loop_clr_fd() we bdput(bdev).
    @@ -933,7 +953,7 @@ static int loop_clr_fd(struct loop_device *lo)
    mutex_unlock(&lo->lo_open_mutex);

    if (lo->lo_flags & LO_FLAGS_PARTSCAN && bdev)
    - ioctl_by_bdev(bdev, BLKRRPART, 0);
    + loop_reread_partitions(lo, bdev);
    lo->lo_flags = 0;
    if (!part_shift)
    lo->lo_disk->flags |= GENHD_FL_NO_PART_SCAN;
    @@ -1008,7 +1028,7 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
    !(lo->lo_flags & LO_FLAGS_PARTSCAN)) {
    lo->lo_flags |= LO_FLAGS_PARTSCAN;
    lo->lo_disk->flags &= ~GENHD_FL_NO_PART_SCAN;
    - ioctl_by_bdev(lo->lo_device, BLKRRPART, 0);
    + loop_reread_partitions(lo, lo->lo_device);
    }

    lo->lo_encrypt_key_size = info->lo_encrypt_key_size;
    --
    1.8.3.1


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