linux-kernel - Re: [PATCH v2] btrfs: add missing check after link_free

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Message-ID: <20191209182543.GQ2734@twin.jikos.cz>
Date:   Mon, 9 Dec 2019 19:25:43 +0100
From:   David Sterba <dsterba@...e.cz>
To:     Dinghao Liu <dinghao.liu@....edu.cn>
Cc:     kjlu@....edu, Chris Mason <clm@...com>,
        Josef Bacik <josef@...icpanda.com>,
        David Sterba <dsterba@...e.com>, linux-btrfs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] btrfs: add missing check after link_free_space

On Mon, Dec 09, 2019 at 11:41:14AM +0800, Dinghao Liu wrote:
> The return value of link_free_space is checked out-sync.
> One branch of an if statement uses an extra check after
> WARN_ON() but its peer branch does not. WARN_ON() does
> not change the control flow, thus only using this check
> might be insufficient.
> 
> Fix this by simply adding a check on ret.
> 
> Signed-off-by: Dinghao Liu <dinghao.liu@....edu.cn>
> --
> Changes in v2:
>   - Add memory free for free space entry.
> ---
>  fs/btrfs/free-space-cache.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/fs/btrfs/free-space-cache.c b/fs/btrfs/free-space-cache.c
> index 3283da419200..ba2e6cea5233 100644
> --- a/fs/btrfs/free-space-cache.c
> +++ b/fs/btrfs/free-space-cache.c
> @@ -2437,6 +2437,10 @@ 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) {
> +					kmem_cache_free(btrfs_free_space_cachep, info);
> +					goto out_lock;
> +				}
>  			} else {
>  				kmem_cache_free(btrfs_free_space_cachep, info);

There are two link_free_space followed by WARN_ON instances in the
function, please remove both.

In the above case, the branches can be merged together so there's not
repeated kmem_cache_free, like

	if (info->bytes)
		ret = link_free_space(...);
	kmem_cache_free(btrfs_free_space_cachep, info);
	if (ret)
		goto out_unlock;