Re: [PATCH 5/8] loop: only take lo_mutex for the first reference in lo_open
From: Jan Kara <jack@suse.cz>
Date: 2022-01-28 13:38:02
On Fri 28-01-22 14:00:19, Christoph Hellwig wrote:
lo_refcnt is only incremented in lo_open and decremented in lo_release, and thus protected by open_mutex. Only take lo_mutex when lo_open is called the first time, as only for the first open there is any affect on the driver state (incremental opens on partitions don't end up in lo_open at all already). Signed-off-by: Christoph Hellwig <hch@lst.de> Tested-by: Darrick J. Wong <djwong@kernel.org>
Looks good. Feel free to add: Reviewed-by: Jan Kara <jack@suse.cz> Honza
quoted hunk ↗ jump to hunk
--- drivers/block/loop.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)diff --git a/drivers/block/loop.c b/drivers/block/loop.c index b58dc95f80d96..f349ddfc0e84a 100644 --- a/drivers/block/loop.c +++ b/drivers/block/loop.c@@ -1725,13 +1725,20 @@ static int lo_open(struct block_device *bdev, fmode_t mode) struct loop_device *lo = bdev->bd_disk->private_data; int err; + /* + * Note: this requires disk->open_mutex to protect against races + * with lo_release. + */ + if (atomic_inc_return(&lo->lo_refcnt) > 1) + return 0; + err = mutex_lock_killable(&lo->lo_mutex); if (err) return err; - if (lo->lo_state == Lo_deleting) + if (lo->lo_state == Lo_deleting) { + atomic_dec(&lo->lo_refcnt); err = -ENXIO; - else - atomic_inc(&lo->lo_refcnt); + } mutex_unlock(&lo->lo_mutex); return err; }-- 2.30.2
-- Jan Kara [off-list ref] SUSE Labs, CR