linux-kernel - Re: [PATCH v3] ext4: Fix bug on in ext4_es_cache_extent as ext4_split_extent

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Message-ID: <20210506101915.GA22189@quack2.suse.cz>
Date:   Thu, 6 May 2021 12:19:15 +0200
From:   Jan Kara <jack@...e.cz>
To:     yebin <yebin10@...wei.com>
Cc:     Jan Kara <jack@...e.cz>, tytso@....edu, adilger.kernel@...ger.ca,
        linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] ext4: Fix bug on in ext4_es_cache_extent as
 ext4_split_extent_at failed

On Thu 06-05-21 16:26:24, yebin wrote:
> Thanks for your suggesttion. If you have no objection to following
> modification, i will send it as V4.
> 
> diff --git a/fs/ext4/extents.c b/fs/ext4/extents.c
> index 77c84d6f1af6..f9cbd11e1eae 100644
> --- a/fs/ext4/extents.c
> +++ b/fs/ext4/extents.c
> @@ -3206,7 +3206,10 @@ static int ext4_split_extent_at(handle_t *handle,
>                 ext4_ext_mark_unwritten(ex2);
> 
>         err = ext4_ext_insert_extent(handle, inode, ppath, &newex, flags);
> -       if (err == -ENOSPC && (EXT4_EXT_MAY_ZEROOUT & split_flag)) {
> +       if (err != -ENOSPC && err != -EDQUOT)
> +                goto out;
> +
> +       if (EXT4_EXT_MAY_ZEROOUT & split_flag) {

You need:

if (err && (EXT4_EXT_MAY_ZEROOUT & split_flag))

there, don't you? You don't want to zero-out if there's no error.

> @@ -3232,22 +3235,23 @@ static int ext4_split_extent_at(handle_t *handle,
> ext4_ext_pblock(&orig_ex));
>                 }
> 
> -               if (err)
> -                       goto fix_extent_len;
> -               /* update the extent length and mark as initialized */
> -               ex->ee_len = cpu_to_le16(ee_len);
> -               ext4_ext_try_to_merge(handle, inode, path, ex);
> -               err = ext4_ext_dirty(handle, inode, path + path->p_depth);
> -               if (err)
> -                       goto fix_extent_len;
> -
> -               /* update extent status tree */
> -               err = ext4_zeroout_es(inode, &zero_ex);
> -
> -               goto out;
> -       } else if (err)
> -               goto fix_extent_len;
> -
> +               if (!err) {
> +                       /* update the extent length and mark as initialized
> */
> +                        ex->ee_len = cpu_to_le16(ee_len);
> +                        ext4_ext_try_to_merge(handle, inode, path, ex);
> +                        err = ext4_ext_dirty(handle, inode, path +
> path->p_depth);
> +                        if (!err)
> +                               /* update extent status tree */
> +                                err = ext4_zeroout_es(inode, &zero_ex);
> +                        /* At here, ext4_ext_try_to_merge maybe already
> merge
> +                         * extent, if fix origin extent length may lead to
> +                         * overwritten.
> +                         */

I'd rephrase the comment as:

/*
 * If we failed at this point, we don't know in which state the extent tree
 * exactly is so don't try to fix length of the original extent as it may do
 * even more damage.
 */


> +                        goto out;
> +                }
> +       }
> +        if (err)
> +                goto fix_extent_len;

And you can move this if (err) before if (!err) above to make code easier
to read and save one indentation level.

>  out:
>         ext4_ext_show_leaf(inode, path);
>         return err;
> 
> 
								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR