Add post_release() block device callback which allows release() block
device callback to schedule an extra cleanup operation while holding
disk->open_mutex and let post_release() callback synchronously perform
that operation without holding disk->open_mutex.
The loop driver needs this callback for synchronously performing autoclear
operation, for some userspace programs (e.g. xfstest) depend on that the
autoclear operation already completes by the moment lo_release() from
close() returns to userspace and immediately call umount() of a partition
containing a backing file which the autoclear operation will close(), but
temporarily dropping disk->open_mutex inside lo_release() in order to avoid
circular locking dependency is considered as a bad approach.
Note that unlike release() callback, post_release() callback is called
every time blkdev_put() is called. That is, the release() callback is
responsible for making it possible for post_release() callback to tell
whether post_release() callback has something to do.
Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
Fixes: 322c4293ecc58110 ("loop: make autoclear operation asynchronous")
Signed-off-by: Tetsuo Handa <penguin-kernel@xxxxxxxxxxxxxxxxxxx>
---
block/bdev.c | 2 ++
include/linux/blkdev.h | 5 +++++
2 files changed, 7 insertions(+)
diff --git a/block/bdev.c b/block/bdev.c
index 8bf93a19041b..0cb638d81a27 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -948,6 +948,8 @@ void blkdev_put(struct block_device *bdev, fmode_t mode)
else
blkdev_put_whole(bdev, mode);
mutex_unlock(&disk->open_mutex);
+ if (bdev->bd_disk->fops->post_release)
+ bdev->bd_disk->fops->post_release(bdev->bd_disk);
module_put(disk->fops->owner);
blkdev_put_no_open(bdev);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index c80cfaefc0a8..b252b1d87471 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1227,6 +1227,11 @@ struct block_device_operations {
* driver.
*/
int (*alternative_gpt_sector)(struct gendisk *disk, sector_t *sector);
+ /*
+ * Special callback for doing post-release callback without
+ * disk->open_mutex held. Used by loop driver.
+ */
+ void (*post_release)(struct gendisk *disk);
};
#ifdef CONFIG_COMPAT
--
2.32.0
