linux-kernel - Re: [PATCH v4 2/5] fs: Check if utf8 encoding is loaded before calling utf8

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Message-ID: <YFziza/VMyzEs4s1@sol.localdomain>
Date:   Thu, 25 Mar 2021 12:21:49 -0700
From:   Eric Biggers <ebiggers@...nel.org>
To:     Shreeya Patel <shreeya.patel@...labora.com>
Cc:     tytso@....edu, adilger.kernel@...ger.ca, jaegeuk@...nel.org,
        chao@...nel.org, krisman@...labora.com, drosen@...gle.com,
        yuchao0@...wei.com, linux-ext4@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net,
        linux-fsdevel@...r.kernel.org, kernel@...labora.com,
        andre.almeida@...labora.com
Subject: Re: [PATCH v4 2/5] fs: Check if utf8 encoding is loaded before
 calling utf8_unload()

On Thu, Mar 25, 2021 at 05:38:08AM +0530, Shreeya Patel wrote:
> utf8_unload is being called if CONFIG_UNICODE is enabled.
> The ifdef block doesn't check if utf8 encoding has been loaded
> or not before calling the utf8_unload() function.
> This is not the expected behavior since it would sometimes lead
> to unloading utf8 even before loading it.
> Hence, add a condition which will check if sb->encoding is NOT NULL
> before calling the utf8_unload().
> 
> Reviewed-by: Gabriel Krisman Bertazi <krisman@...labora.com>
> Signed-off-by: Shreeya Patel <shreeya.patel@...labora.com>
> ---
>  fs/ext4/super.c | 6 ++++--
>  fs/f2fs/super.c | 9 ++++++---
>  2 files changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index ad34a37278cd..e438d14f9a87 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -1259,7 +1259,8 @@ static void ext4_put_super(struct super_block *sb)
>  	fs_put_dax(sbi->s_daxdev);
>  	fscrypt_free_dummy_policy(&sbi->s_dummy_enc_policy);
>  #ifdef CONFIG_UNICODE
> -	utf8_unload(sb->s_encoding);
> +	if (sb->s_encoding)
> +		utf8_unload(sb->s_encoding);
>  #endif
>  	kfree(sbi);
>  }


What's the benefit of this change?  utf8_unload is a no-op when passed a NULL
pointer; why not keep it that way?

- Eric