linux-kernel - Re: [PATCH v2] sysctl: Reduce dput(child) calls in proc_sys_fill

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Message-ID: <fpyvxkkhyv7gqbwayxmcglf2jh6gs65brbtojxxtpief4nm35g@l2jq7oab7p3p>
Date: Mon, 28 Oct 2024 10:23:02 +0100
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>, 
	Kees Cook <kees@...nel.org>, Luis Chamberlain <mcgrof@...nel.org>, 
	LKML <linux-kernel@...r.kernel.org>, kernel-janitors@...r.kernel.org, 
	Joel Granados <j.granados@...sung.com>
Subject: Re: [PATCH v2] sysctl: Reduce dput(child) calls in
 proc_sys_fill_cache()

On Wed, Oct 23, 2024 at 05:27:11PM +0200, Markus Elfring wrote:
> From: Markus Elfring <elfring@...rs.sourceforge.net>
> Date: Wed, 23 Oct 2024 16:54:59 +0200
> 
> Replace two dput(child) calls with one that occurs immediately before
> the IS_ERR evaluation. This transformation can be performed because
> dput() gets called regardless of the value returned by IS_ERR(res).
> 
> This issue was transformed by using a script for the
> semantic patch language like the following.
> <SmPL>
Aren't you missing a "virtual patch" here?

Is there another way to run it besides this command:
make coccicheck MODE=patch SPFLAGS="--in-place --include-headers --smpl-spacing --jobs=16" COCCI=SCRIPT

Best
> @extended_adjustment@
> expression e, f != { mutex_unlock }, x, y;
> @@
> +f(e);
>  if (...)
>  {
>  <+... when != \( e = x \| y(..., &e, ...) \)
> -   f(e);
>  ...+>
>  }
> -f(e);
> </SmPL>
> 
> Signed-off-by: Markus Elfring <elfring@...rs.sourceforge.net>
> ---
> 
> V2:
> * This update suggestion was rebased on source files of the software
>   “Linux next-20241023”.
> 
> * The change description was adjusted according to the wording preferences
>   by Joel Granados.
> 
> * An SmPL script example was appended.
> 
> 
>  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 9b9dfc450cb3..b277a1ca392e 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;
>  			}
>  		}
> --
> 2.47.0
> 

-- 

Joel Granados