[PATCH 4/8] loop: only take lo_mutex for the last reference in lo_release
From: Christoph Hellwig <hch@lst.de>
Date: 2022-01-28 13:00:41
Subsystem:
block layer, the rest · Maintainers:
Jens Axboe, Linus Torvalds
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_release actually takes action for the final release. Signed-off-by: Christoph Hellwig <hch@lst.de> Tested-by: Darrick J. Wong <djwong@kernel.org> --- drivers/block/loop.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index d3a7f281ce1b6..b58dc95f80d96 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c@@ -1740,10 +1740,14 @@ static void lo_release(struct gendisk *disk, fmode_t mode) { struct loop_device *lo = disk->private_data; - mutex_lock(&lo->lo_mutex); - if (atomic_dec_return(&lo->lo_refcnt)) - goto out_unlock; + /* + * Note: this requires disk->open_mutex to protect against races + * with lo_open. + */ + if (!atomic_dec_and_test(&lo->lo_refcnt)) + return; + mutex_lock(&lo->lo_mutex); if (lo->lo_flags & LO_FLAGS_AUTOCLEAR) { if (lo->lo_state != Lo_bound) goto out_unlock;
--
2.30.2