Commit 02ee654d authored May 17, 2018 by Anand Jain Committed by David Sterba May 17, 2018

btrfs: fix crash when trying to resume balance without the resume flag



We set the BTRFS_BALANCE_RESUME flag in the btrfs_recover_balance()
only, which isn't called during the remount. So when resuming from
the paused balance we hit the 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 filesystem:

  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().

CC: stable@vger.kernel.org # 4.4+
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent fe816d0f

fs/btrfs/volumes.c

+9 −0

Original line number	Diff line number	Diff line
		@@ -4052,6 +4052,15 @@ int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info)
		return 0;
		}

		/*
		* A ro->rw remount sequence should continue with the paused balance
		* regardless of who pauses it, system or the user as of now, so set
		* the resume flag.
		*/
		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);
		}