Re: [PATCH 6/8] btrfs: clear BTRFS_ROOT_DEAD_RELOC_TREE before dropping the reloc root

Qu Wenruo
2020-03-05T11:41:41Z

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On 2020/3/5 上午12:18, Josef Bacik wrote:
> We were doing the clear dance for the reloc root after doing the drop of
> the reloc root, which means we have a giant window where we could miss
> having BTRFS_ROOT_DEAD_RELOC_TREE unset and the reloc_root == NULL.

Still, I can't see the problem where we have BTRFS_ROOT_DEAD_RELOC_TREE
and reloc_root == NULL.

IMHO, that would cause anything wrong. Or is there anything I missed?

Thanks,
Qu
>
> Signed-off-by: Josef Bacik <josef@toxicpanda.com>
> ---
> fs/btrfs/relocation.c | 13 +++++++------
> 1 file changed, 7 insertions(+), 6 deletions(-)
>
> diff --git a/fs/btrfs/relocation.c b/fs/btrfs/relocation.c
> index 53509c367eff..ceb90d152cdd 100644
> --- a/fs/btrfs/relocation.c
> +++ b/fs/btrfs/relocation.c
> @@ -2291,18 +2291,19 @@ static int clean_dirty_subvols(struct reloc_control *rc)
>
> list_del_init(&root->reloc_dirty_list);
> root->reloc_root = NULL;
> - if (reloc_root) {
> -
> - ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
> - if (ret2 < 0 && !ret)
> - ret = ret2;
> - }
> /*
> * Need barrier to ensure clear_bit() only happens after
> * root->reloc_root = NULL. Pairs with have_reloc_root.
> */
> smp_wmb();
> clear_bit(BTRFS_ROOT_DEAD_RELOC_TREE, &root->state);
> +
> + if (reloc_root) {
> +
> + ret2 = btrfs_drop_snapshot(reloc_root, NULL, 0, 1);
> + if (ret2 < 0 && !ret)
> + ret = ret2;
> + }
> btrfs_put_root(root);
> } else {
> /* Orphan reloc tree, just clean it up */
>

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