[PATCH] btrfs: fix BUG trying to resume balance without resume flag

[PATCH] btrfs: fix BUG trying to resume balance without resume flag

[Anand Jain]

We set the BTRFS_BALANCE_RESUME flag in the btrfs_recover_balance(),
which is not called during the remount. So when resuming from the
paused balance we hit BUG.

 kernel: kernel BUG at fs/btrfs/volumes.c:3890!
 ::
 kernel:  balance_kthread+0x51/0x60 [btrfs]
 kernel:  kthread+0x111/0x130
 ::
 kernel: RIP: btrfs_balance+0x12e1/0x1570 [btrfs] RSP: ffffba7d0090bde8

Reproducer:
  On a mounted BTRFS.

  btrfs balance start --full-balance /btrfs
  btrfs balance pause /btrfs
  mount -o remount,ro /dev/sdb /btrfs
  mount -o remount,rw /dev/sdb /btrfs

To fix this set the BTRFS_BALANCE_RESUME flag in btrfs_resume_balance_async()
instead of btrfs_recover_balance().

Signed-off-by: Anand Jain <anand.jain@oracle.com>
---
 fs/btrfs/volumes.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 66d2ed96aef1..9c29fdca9075 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -3963,6 +3963,10 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
 		return 0;
 	}
 
+	spin_lock(&fs_info->balance_lock);
+	fs_info->balance_ctl->flags |= BTRFS_BALANCE_RESUME;
+	spin_unlock(&fs_info->balance_lock);
+
 	tsk = kthread_run(balance_kthread, fs_info, "btrfs-balance");
 	return PTR_ERR_OR_ZERO(tsk);
 }
@@ -4004,7 +4008,6 @@ int btrfs_recover_balance(struct btrfs_fs_info *fs_info)
 
 	bctl->fs_info = fs_info;
 	bctl->flags = btrfs_balance_flags(leaf, item);
-	bctl->flags |= BTRFS_BALANCE_RESUME;
 
 	btrfs_balance_data(leaf, item, &disk_bargs);
 	btrfs_disk_balance_args_to_cpu(&bctl->data, &disk_bargs);
-- 
2.7.0