Hi Josef,
2014-03-28 2:56 GMT+08:00 Josef Bacik <jbacik@xxxxxx>:
> This was done to allow NO_COW to continue to be NO_COW after relocation but it
> is not right. When relocating we will convert blocks to FULL_BACKREF that we
> relocate. We can leave some of these full backref blocks behind if they are not
> cow'ed out during the relocation, like if we fail the relocation with ENOSPC and
> then just drop the reloc tree. Then when we go to cow the block again we won't
> lookup the extent flags because we won't think there has been a snapshot
> recently which means we will do our normal ref drop thing instead of adding back
> a tree ref and dropping the shared ref. This will cause btrfs_free_extent to
> blow up because it can't find the ref we are trying to free. This was found
> with my ref verifying tool. Thanks,
Could we pass error into merge_reloc_roots() something like this:
merge_reloc_roots(struct reloc_control *rc, int err)
and we only skip reset root's last snapshot if @err is not 0. I think
it is meaningful
to allow NO_COW to continue after relocation.
Thanks,
Wang
>
> Signed-off-by: Josef Bacik <jbacik@xxxxxx>
> ---
> fs/btrfs/relocation.c | 21 ---------------------
> 1 file changed, 21 deletions(-)
>
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index ec00777..f026a82 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2318,7 +2318,6 @@ void free_reloc_roots(struct list_head *list)
> static noinline_for_stack
> int merge_reloc_roots(struct reloc_control *rc)
> {
> - struct btrfs_trans_handle *trans;
> struct btrfs_root *root;
> struct btrfs_root *reloc_root;
> u64 last_snap;
> @@ -2376,26 +2375,6 @@ again:
> list_add_tail(&reloc_root->root_list,
> &reloc_roots);
> goto out;
> - } else if (!ret) {
> - /*
> - * recover the last snapshot tranid to avoid
> - * the space balance break NOCOW.
> - */
> - root = read_fs_root(rc->extent_root->fs_info,
> - objectid);
> - if (IS_ERR(root))
> - continue;
> -
> - trans = btrfs_join_transaction(root);
> - BUG_ON(IS_ERR(trans));
> -
> - /* Check if the fs/file tree was snapshoted or not. */
> - if (btrfs_root_last_snapshot(&root->root_item) ==
> - otransid - 1)
> - btrfs_set_root_last_snapshot(&root->root_item,
> - last_snap);
> -
> - btrfs_end_transaction(trans, root);
> }
> }
>
> --
> 1.8.3.1
>
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