[PATCH v2] dm: restore synchronous close of device mapper block device

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From: Ming Lei <ming.lei@xxxxxxxxxx>

'dmsetup remove' and 'dmsetup remove_all' require synchronous bdev
release. Otherwise dm_lock_for_deletion() may return -EBUSY if the open
count is > 0, because the open count is dropped in dm_blk_close()
which occurs after fput() completes.

So if dm_blk_close() is delayed because of asynchronous fput(), this
device mapper device is skipped during remove, which is a regression.

Fix the issue by using __fput_sync().

Also: DM device removal has long supported being made asynchronous by
setting the DMF_DEFERRED_REMOVE flag on the DM device. So leverage
using async fput() in close_table_device() if DMF_DEFERRED_REMOVE flag
is set.

Reported-by: Zhong Changhui <czhong@xxxxxxxxxx>
Fixes: a28d893eb327 ("md: port block device access to file")
Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
[snitzer: editted commit header, use fput() if DMF_DEFERRED_REMOVE set]
Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxx>
 drivers/md/dm.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 56aa2a8b9d71..7d0746b37c8e 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -765,7 +765,7 @@ static struct table_device *open_table_device(struct mapped_device *md,
 	return td;
-	fput(bdev_file);
+	__fput_sync(bdev_file);
 	return ERR_PTR(r);
@@ -778,7 +778,13 @@ static void close_table_device(struct table_device *td, struct mapped_device *md
 	if (md->disk->slave_dir)
 		bd_unlink_disk_holder(td->dm_dev.bdev, md->disk);
-	fput(td->dm_dev.bdev_file);
+	/* Leverage async fput() if DMF_DEFERRED_REMOVE set */
+	if (unlikely(test_bit(DMF_DEFERRED_REMOVE, &md->flags)))
+		fput(td->dm_dev.bdev_file);
+	else
+		__fput_sync(td->dm_dev.bdev_file);

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