linux-kernel - Re: [PATCH net] netpoll: guard __netpoll_send

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Message-ID: <20250305-dancing-pretty-kestrel-b269df@leitao>
Date: Wed, 5 Mar 2025 10:51:50 -0800
From: Breno Leitao <leitao@...ian.org>
To: Andrew Lunn <andrew@...n.ch>
Cc: Jakub Kicinski <kuba@...nel.org>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
	Simon Horman <horms@...nel.org>, Amerigo Wang <amwang@...hat.com>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel-team@...a.com
Subject: Re: [PATCH net] netpoll: guard __netpoll_send_skb() with RCU read
 lock

On Wed, Mar 05, 2025 at 05:09:14PM +0100, Andrew Lunn wrote:
> On Wed, Mar 05, 2025 at 01:09:49AM -0800, Breno Leitao wrote:
> > Hello Jakub,
> > 
> > On Tue, Mar 04, 2025 at 05:47:32PM -0800, Jakub Kicinski wrote:
> > > On Mon, 03 Mar 2025 03:44:12 -0800 Breno Leitao wrote:
> > > > +	guard(rcu)();
> > > 
> > > Scoped guards if you have to.
> > > Preferably just lock/unlock like a normal person..
> > 
> > Sure, I thought that we would be moving to scoped guards all across the
> > board, at least that was my reading for a similar patch I sent a while
> > ago:
> > 
> > 	https://lore.kernel.org/all/20250224123016.GA17456@noisy.programming.kicks-ass.net/
> > 
> > Anyway, in which case should I use scoped guard instead of just being
> > like a normal person?
> 
> https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html
> 
>   Section 1.6.5: Using device-managed and cleanup.h constructs
> 
>   Netdev remains skeptical about promises of all “auto-cleanup” APIs,
>   including even devm_ helpers, historically. They are not the
>   preferred style of implementation, merely an acceptable one.
> 
>   Use of guard() is discouraged within any function longer than 20
>   lines, scoped_guard() is considered more readable. Using normal
>   lock/unlock is still (weakly) preferred.
> 
>   Low level cleanup constructs (such as __free()) can be used when
>   building APIs and helpers, especially scoped iterators. However,
>   direct use of __free() within networking core and drivers is
>   discouraged. Similar guidance applies to declaring variables
>   mid-function.
> 
> So you need to spend time to find out what each subsystems view is on
> various APIs.

That is clear. thanks for the heads-up!

--breno