Re: [PATCH v2] btrfs: Gracefully handle errors in btrfs_qgroup_trace_extent_post

[Qu Wenruo]

On 2018年01月29日 15:44, Nikolay Borisov wrote:
> Running generic/019 with qgroups on the scratch device enabled is
> almost guaranteed to trigger the BUG_ON in btrfs_free_tree_block. It's
> supposed to trigger only on -ENOMEM, in reality, however, it's possible
> to get -EIO from btrfs_qgroup_trace_extent_post. This function just
> finds the roots of the extent being tracked and sets the qrecord->old_roots
> list. If this operation fails nothing critical happens except the
> quota accounting can be considered wrong. In such case just set the
> INCONSISTENT flag for the quota and print a warning.
> 
> Signed-off-by: Nikolay Borisov <nbori...@suse.com>
> ---
> 
> V2: 
>  * Always print a warning if btrfs_qgroup_trace_extent_post fails 
>  * Set quota inconsistent flag if btrfs_qgroup_trace_extent_post fails
> 
>  fs/btrfs/delayed-ref.c | 7 +++++--
>  fs/btrfs/qgroup.c      | 6 ++++--
>  2 files changed, 9 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
> index a1a40cf382e3..5b2789a28a13 100644
> --- a/fs/btrfs/delayed-ref.c
> +++ b/fs/btrfs/delayed-ref.c
> @@ -820,8 +820,11 @@ int btrfs_add_delayed_tree_ref(struct btrfs_fs_info 
> *fs_info,
>                            num_bytes, parent, ref_root, level, action);
>       spin_unlock(&delayed_refs->lock);
>  
> -     if (qrecord_inserted)
> -             return btrfs_qgroup_trace_extent_post(fs_info, record);
> +     if (qrecord_inserted) {
> +             int ret = btrfs_qgroup_trace_extent_post(fs_info, record);
> +             if (ret < 0)
> +                     btrfs_warn(fs_info, "Error accounting new delayed refs 
> extent (err code: %d). Quota inconsistent", ret);

Sorry that I didn't point it out in previous review, there are 2 callers
in delayed-ref.c using btrfs_qgroup_trace_extent_post().

One is the one you're fixing, and the other one is
btrfs_add_delayed_data_ref().

So it would be even better if the warning message can be integrated into
btrfs_qgroup_trace_extent_post().

Also btrfs_qgroup_trace_extent_post() also needs to ignore the return
value from btrfs_qgroup_trace_extent_post().

Thanks,
Qu

> +     }
>       return 0;
>  
>  free_head_ref:
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index b2ab5f795816..33f9dba44e92 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -1440,8 +1440,10 @@ int btrfs_qgroup_trace_extent_post(struct 
> btrfs_fs_info *fs_info,
>       int ret;
>  
>       ret = btrfs_find_all_roots(NULL, fs_info, bytenr, 0, &old_root, false);
> -     if (ret < 0)
> +     if (ret < 0) {
> +             fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
>               return ret;
> +     }
>  
>       /*
>        * Here we don't need to get the lock of
> @@ -2933,7 +2935,7 @@ static int __btrfs_qgroup_release_data(struct inode 
> *inode,
>       if (free && reserved)
>               return qgroup_free_reserved_data(inode, reserved, start, len);
>       extent_changeset_init(&changeset);
> -     ret = clear_record_extent_bits(&BTRFS_I(inode)->io_tree, start, 
> +     ret = clear_record_extent_bits(&BTRFS_I(inode)->io_tree, start,
>                       start + len -1, EXTENT_QGROUP_RESERVED, &changeset);
>       if (ret < 0)
>               goto out;
> 

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