btrfs: Fix flush bio leak

lorddoskias · kdave · commit beed9263f400 · 2018-01-02T18:00:13.000+01:00
Commit e0ae999 ("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: e0ae999 ("btrfs: preallocate device flush bio") Signed-off-by: Nikolay Borisov <nborisov@suse.com> Reviewed-by: Liu Bo <bo.li.liu@oracle.com> Reviewed-by: David Sterba <dsterba@suse.com> Signed-off-by: David Sterba <dsterba@suse.com>
diff --git 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);

Original file line number	Diff line number	Diff line change
`@@ -237,7 +237,6 @@ static struct btrfs_device *__alloc_device(void)`
`237`	`237`	`kfree(dev);`
`238`	`238`	`return ERR_PTR(-ENOMEM);`
`239`	`239`	`}`
`240`		`- bio_get(dev->flush_bio);`
`241`	`240`
`242`	`241`	`INIT_LIST_HEAD(&dev->dev_list);`
`243`	`242`	`INIT_LIST_HEAD(&dev->dev_alloc_list);`