netdev - [PATCH v1 net-next] checkpatch: Discourage a new use of rtnl

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Message-ID: <20250211070447.25001-1-kuniyu@amazon.com>
Date: Tue, 11 Feb 2025 16:04:47 +0900
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: "David S. Miller" <davem@...emloft.net>, Eric Dumazet
	<edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>
CC: Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>,
	Dwaipayan Ray <dwaipayanray1@...il.com>, Lukas Bulwahn
	<lukas.bulwahn@...il.com>, Kuniyuki Iwashima <kuniyu@...zon.com>, "Kuniyuki
 Iwashima" <kuni1840@...il.com>, <netdev@...r.kernel.org>
Subject: [PATCH v1 net-next] checkpatch: Discourage a new use of rtnl_lock() variants.

rtnl_lock() is a "Big Kernel Lock" in the networking slow path
and still serialises most of RTM_(NEW|DEL|SET)* rtnetlink requests.

Commit 76aed95319da ("rtnetlink: Add per-netns RTNL.") started a
very large, in-progress, effort to make the RTNL lock scope per
network namespace.

However, there are still some patches that newly use rtnl_lock(),
which is now discouraged, and we need to revisit it later.

Let's warn about the case by checkpatch.

The target functions are as follows:

  * rtnl_lock()
  * rtnl_trylock()
  * rtnl_lock_interruptible()
  * rtnl_lock_killable()

and the warning will be like:

  WARNING: A new use of rtnl_lock() variants is discouraged, try to use rtnl_net_lock(net) variants
  #18: FILE: net/core/rtnetlink.c:79:
  +	rtnl_lock();

Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>
---
It would be nice if this patch goes through net-next.git to catch
new rtnl_lock() users by netdev CI.
---
 scripts/checkpatch.pl | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 7b28ad331742..09d5420436cc 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -6995,6 +6995,12 @@ sub process {
 #			}
 #		}
 
+# A new use of rtnl_lock() is discouraged as it's being converted to rtnl_net_lock(net).
+		if ($line =~ /^\+.*\brtnl_(try)?lock(_interruptible|_killable)?\(\)/) {
+			WARN("rtnl_lock()",
+			     "A new use of rtnl_lock() variants is discouraged, try to use rtnl_net_lock(net) variants\n" . $herecurr);
+		}
+
 # strcpy uses that should likely be strscpy
 		if ($line =~ /\bstrcpy\s*\(/) {
 			WARN("STRCPY",
-- 
2.39.5 (Apple Git-154)