4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nikolay Borisov <nbori...@suse.com>


[ Upstream commit beed9263f4000c48a5c48912f26576f6fa091181 ]

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 <nbori...@suse.com>
Reviewed-by: Liu Bo <bo.li....@oracle.com>
Reviewed-by: David Sterba <dste...@suse.com>
Signed-off-by: David Sterba <dste...@suse.com>
Signed-off-by: Sasha Levin <alexander.le...@verizon.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>
---
 fs/btrfs/volumes.c |    1 -
 1 file changed, 1 deletion(-)

--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -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);


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