[PATCH AUTOSEL for 4.14 070/110] btrfs: Fix flush bio leak

[Sasha Levin]

From: Nikolay Borisov <nborisov@xxxxxxxx>

[ 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 <nborisov@xxxxxxxx>
Reviewed-by: Liu Bo <bo.li.liu@xxxxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
---
 fs/btrfs/volumes.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 4006b2a1233d..bc534fafacf9 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -236,7 +236,6 @@ static struct btrfs_device *__alloc_device(void)
 		kfree(dev);
 		return ERR_PTR(-ENOMEM);
 	}
-	bio_get(dev->flush_bio);
 
 	INIT_LIST_HEAD(&dev->dev_list);
 	INIT_LIST_HEAD(&dev->dev_alloc_list);
-- 
2.11.0