Commit e0ae99941423 ("btrfs: preallocate device flush bio") reworked the way the flush bio is allocated and used. Concretely it allocates the bio in __alloc_device and then re-uses it multiple times with a very simple endio routine that just calls complete() without consuming a reference. Allocated bios by default come with a ref count of 1, which is then consumed by the endio routine (or not, in which case they should be bio_put by the caller). The way the impleementation works now is that the flush bio has a refcount of 2 and we only ever bio_put it once, leaving it to hang indefinitely. Fix this by removing the extra bio_get in __alloc_device.

Fixes e0ae99941423 ("btrfs: preallocate device flush bio")

Signed-off-by Nikolay Borisov <[email protected]>

Reviewed-by Liu Bo <[email protected]>

Reviewed-by David Sterba <[email protected]>

Signed-off-by David Sterba <[email protected]>

Signed-off-by Sasha Levin <[email protected]>

Signed-off-by Greg Kroah-Hartman <[email protected]>

---
 fs/btrfs/volumes.c |    1 -
 1 file changed, 1 deletion(-)

fs/btrfs/volumes.c +0 -1

@@ -236,7 +236,6 @@ static struct btrfs_device *__alloc_devi
 		kfree(dev);
 		return ERR_PTR(-ENOMEM);
 	}
-	bio_get(dev->flush_bio);
 
 	INIT_LIST_HEAD(&dev->dev_list);
 	INIT_LIST_HEAD(&dev->dev_alloc_list);

Patches currently in stable-queue which might be from [email protected] are

queue-4.14/btrfs-fix-flush-bio-leak.patch