On Fri, Apr 10, 2020 at 11:42:48AM -0400, Josef Bacik wrote:
> I made a mistake with my previous fix, I assumed that we didn't need to
> mess with the reloc roots once we were out of the part of relocation
> where we are actually moving the extents.
>
> The subtle thing that I missed is that btrfs_init_reloc_root() also
> updates the last_trans for the reloc root when we do
> btrfs_record_root_in_trans() for the corresponding fs_root. I've added
> a comment to make sure future me doesn't make this mistake again.
>
> This showed up as a WARN_ON() in btrfs_copy_root() because our
> last_trans didn't == the current transid. This could happen if we
> snapshotted a fs root with a reloc root after we set
> rc->create_reloc_tree = 0, but before we actually merge the reloc root.
>
> Fixes: 2abc726ab4b8 ("btrfs: do not init a reloc root if we aren't relocating")
> Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
Added to misc-next with the stacktrace.
