btrfs: Fix flush bio leak

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]>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index d48b24e54366f3c2c6892d6a7bb0f286c02cb8c2..94d28f54983735adb1d62b7d1496a263df30fef7 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -237,7 +237,6 @@ 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);