linux-kernel - Re: [PATCH] fs: Fix a missing check bug

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Date:   Sat, 7 Dec 2019 17:16:10 +0000
From:   Filipe Manana <fdmanana@...il.com>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     kjlu@....edu, pakki001@....edu, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>,
        linux-btrfs <linux-btrfs@...r.kernel.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs: Fix a missing check bug

On Sat, Dec 7, 2019 at 3:03 PM Dinghao Liu <dinghao.liu@....edu.cn> wrote:
>
> The return value of link_free_space(ctl, info) is checked out-sync. Only one branch of an if statement checks this return value after WARN_ON(ret).
>
> Since this path pair is similar in semantic, there might be a missing check bug.
>
> Fix this by simply adding a check on ret.
>
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> ---
>  fs/btrfs/free-space-cache.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 3283da419200..acbb3a59d344 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -2437,6 +2437,8 @@ int btrfs_remove_free_space(struct btrfs_block_group *block_group,
>                         if (info->bytes) {
>                                 ret = link_free_space(ctl, info);
>                                 WARN_ON(ret);
> +                               if (ret)

I think the WARN_ON() can go away as well.
The only possible error is -EEXIST, coming from tree_insert_offset().
When that happens tree_insert_offset() already emits a warning.

Also, the free space entry needs to be freed, otherwise we leak
memory. So it should be something like this:

if (ret) {
    kmem_cache_free(btrfs_free_space_cachep, info);
    goto out_unlock;
}

Further the subject should be prefixed with "btrfs: " and not "fs: ",
since this is a btrfs specific patch.
Something like the following for example:

"btrfs: add missing error handling when removing free space"

Thanks.

> +                                       goto out_lock;
>                         } else {
>                                 kmem_cache_free(btrfs_free_space_cachep, info);
>                         }
> --
> 2.21.0 (Apple Git-122)
>


-- 
Filipe David Manana,

“Whether you think you can, or you think you can't — you're right.”