linux-kernel - Re: [PATCH] sysctl: Reduce dput(child) calls in proc_sys_fill

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Message-ID: <y27xv53nb5rqg4ozske4efdoh2omzryrmflkg6lhg2sx3ka3lf@gmqinxx5ta62>
Date: Wed, 23 Oct 2024 13:11:29 +0200
From: Joel Granados <joel.granados@...nel.org>
To: Markus Elfring <Markus.Elfring@....de>
Cc: linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>, 
	Joel Granados <j.granados@...sung.com>, Kees Cook <kees@...nel.org>, 
	Luis Chamberlain <mcgrof@...nel.org>, LKML <linux-kernel@...r.kernel.org>, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] sysctl: Reduce dput(child) calls in proc_sys_fill_cache()

On Thu, Sep 26, 2024 at 10:20:34AM +0200, Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Thu, 26 Sep 2024 10:10:33 +0200
> 
> A dput(child) call was immediately used after an error pointer check
> for a d_splice_alias() call in this function implementation.
> Thus call such a function instead directly before the check.
This message reads funny, please re-write for your v2. Here is how I would write
it.

"
Replace two dput(child) calls with one that occurs immediately before the IS_ERR
evaluation. This is ok because dput gets called regardless of the value returned
by IS_ERR(res).
"

> 
> This issue was transformed by using the Coccinelle software.
How long is the coccinelle script? If it is a reasonable size, can you please
append it to the commit message. If in doubt of what "reasonable" means, just
share it to the list before doing your V2.

> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
>  fs/proc/proc_sysctl.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index d11ebc055ce0..97547de58218 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -698,11 +698,11 @@ static bool proc_sys_fill_cache(struct file *file,
>  			res = d_splice_alias(inode, child);
>  			d_lookup_done(child);
>  			if (unlikely(res)) {
> -				if (IS_ERR(res)) {
> -					dput(child);
> -					return false;
> -				}
>  				dput(child);
> +
> +				if (IS_ERR(res))
> +					return false;
> +
>  				child = res;
>  			}
>  		}
> --
> 2.46.1
> 

-- 

Joel Granados