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

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Message-ID: <582379a6-dea3-482f-86e4-259d4b23204e@web.de>
Date: Wed, 23 Oct 2024 17:27:11 +0200
From: Markus Elfring <Markus.Elfring@....de>
To: linux-fsdevel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>,
 Joel Granados <joel.granados@...nel.org>, Kees Cook <kees@...nel.org>,
 Luis Chamberlain <mcgrof@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>, kernel-janitors@...r.kernel.org,
 Joel Granados <j.granados@...sung.com>
Subject: [PATCH v2] sysctl: Reduce dput(child) calls in proc_sys_fill_cache()

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>
@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