netdev - Re: [PATCH v2 net-next] checkpatch: Discourage a new use of rtnl

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Message-ID: <c25c5efe-6835-44fb-9937-87bf25368a97@intel.com>
Date: Fri, 14 Feb 2025 10:24:46 +0100
From: Mateusz Polchlopek <mateusz.polchlopek@...el.com>
To: Kuniyuki Iwashima <kuniyu@...zon.com>, "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 <kuni1840@...il.com>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH v2 net-next] checkpatch: Discourage a new use of
 rtnl_lock() variants.



On 2/14/2025 5:54 AM, Kuniyuki Iwashima wrote:
> 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>
> Reviewed-by: Simon Horman <horms@...nel.org>
> ---
> v2:
>    * Remove unnecessary "^\+.*"
>    * Match "rtnl_lock	 ()"
> 
> v1: https://lore.kernel.org/netdev/20250211070447.25001-1-kuniyu@amazon.com/
> ---
>   scripts/checkpatch.pl | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
> index 7b28ad331742..eca4f082ac3f 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)?\s*\(\)/) {
> +			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",

Reviewed-by: Mateusz Polchlopek <mateusz.polchlopek@...el.com>