dm: restore synchronous close of device mapper block device

'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@redhat.com>
Fixes: a28d893e ("md: port block device access to file")
Suggested-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
[snitzer: editted commit header, use fput() if DMF_DEFERRED_REMOVE set]
Signed-off-by: Mike Snitzer <snitzer@kernel.org>

drivers/md/dm.c

@@ -765,7 +765,7 @@ static struct table_device *open_table_device(struct mapped_device *md,
 	return td;
 
 out_blkdev_put:
-	fput(bdev_file);
+	__fput_sync(bdev_file);
 out_free_td:
 	kfree(td);
 	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);
+
+	/* 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);
+
 	put_dax(td->dm_dev.dax_dev);
 	list_del(&td->list);
 	kfree(td);