linux-kernel - Re: [PATCH net 2/2] netpoll: Use rcu_access_pointer() in netpoll_poll

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Message-ID: <20241118-bipedal-beryl-peccary-ed32da@leitao>
Date: Mon, 18 Nov 2024 07:37:43 -0800
From: Breno Leitao <leitao@...ian.org>
To: Michal Kubiak <michal.kubiak@...el.com>
Cc: "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>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Stephen Hemminger <stephen@...workplumber.org>,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	paulmck@...nel.org
Subject: Re: [PATCH net 2/2] netpoll: Use rcu_access_pointer() in
 netpoll_poll_lock

On Mon, Nov 18, 2024 at 01:20:30PM +0100, Michal Kubiak wrote:
> On Mon, Nov 18, 2024 at 03:15:18AM -0800, Breno Leitao wrote:
> > The ndev->npinfo pointer in netpoll_poll_lock() is RCU-protected but is
> > being accessed directly for a NULL check. While no RCU read lock is held
> > in this context, we should still use proper RCU primitives for
> > consistency and correctness.
> > 
> > Replace the direct NULL check with rcu_access_pointer(), which is the
> > appropriate primitive when only checking for NULL without dereferencing
> > the pointer. This function provides the necessary ordering guarantees
> > without requiring RCU read-side protection.
> > 
> > Signed-off-by: Breno Leitao <leitao@...ian.org>
> > Fixes: bea3348eef27 ("[NET]: Make NAPI polling independent of struct net_device objects.")
> 
> nitpick: As for the first patch - please check the tags order.
> 
> Thanks,
> Reviewed-by: Michal Kubiak <michal.kubiak@...el.com>

Thanks for the review.

I am not planning to resend it now, since I think maintainer's tooling will
reorder that.

If that is not true, I am more than happy to resend fixing the order.

Thanks
Breno