linux-kernel - Re: [patch] net, bcmgenet: Fix locking of netpoll facing functions

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Message-ID: <1d439b1961a4f6b019e2cc56977e0860b3a7b937.camel@gmx.de>
Date: Fri, 29 Aug 2025 04:40:54 +0200
From: Mike Galbraith <efault@....de>
To: Florian Fainelli <florian.fainelli@...adcom.com>, lkml
	 <linux-kernel@...r.kernel.org>
Cc: Doug Berger <opendmb@...il.com>, Breno Leitao <leitao@...ian.org>
Subject: Re: [patch] net, bcmgenet: Fix locking of netpoll facing functions

On Thu, 2025-08-28 at 11:59 -0700, Florian Fainelli wrote:
> On 8/26/25 01:24, Mike Galbraith wrote:
> > Lockdep reports ring->lock to not be irq safe during netpoll/netconsole
> > session, resulting in a potential deadlock scenario.
> > 
> >   Chain exists of:
> >     &host->lock --> target_list_lock --> &ring->lock
> >    Possible interrupt unsafe locking scenario:
> >          CPU0                    CPU1
> >          ----                    ----
> >     lock(&ring->lock);
> >                                  local_irq_disable();
> >                                  lock(&host->lock);
> >                                  lock(target_list_lock);
> >     <Interrupt>
> >       lock(&host->lock);
> >    *** DEADLOCK ***
> > 
> > Prevent that via use of irqsave/restore spinlock variant when polling.
> > 
> > Signed-off-by: Mike Galbraith <efault@....de>
> 
> Your patch did not make it to the adequate mailing list which should be 
> at least netdev@...r.kernel.org. This is effectively a partial revert of 
> b0447ecb533270cf857ebee1133cb8ff67115423 ("net: bcmgenet: relax lock 
> constraints to reduce IRQ latency") therefore I would want Doug to chime 
> in and review this.

Ah, just drop it, he'll likely do something way better.

	-Mike