netdev - Re: [PATCH v2] igb: Fix watchdog

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Message-ID: <20250609161039.00c73103@kernel.org>
Date: Mon, 9 Jun 2025 16:10:39 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Ian Ray <ian.ray@...ealthcare.com>
Cc: horms@...nel.org, Tony Nguyen <anthony.l.nguyen@...el.com>, Przemek
 Kitszel <przemyslaw.kitszel@...el.com>, Andrew Lunn
 <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, Eric
 Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 brian.ruley@...ealthcare.com, intel-wired-lan@...ts.osuosl.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] igb: Fix watchdog_task race with shutdown

On Mon, 9 Jun 2025 09:32:58 +0300 Ian Ray wrote:
> On Thu, Jun 05, 2025 at 06:43:39PM -0700, Jakub Kicinski wrote:
> > On Tue,  3 Jun 2025 11:09:49 +0300 Ian Ray wrote:  
> > >       set_bit(__IGB_DOWN, &adapter->state);
> > > +     timer_delete_sync(&adapter->watchdog_timer);
> > > +     timer_delete_sync(&adapter->phy_info_timer);
> > > +
> > > +     cancel_work_sync(&adapter->watchdog_task);  
> > 
> > This doesn't look very race-proof as watchdog_task
> > can schedule the timer as its last operation?  
> 
> Thanks for the reply.  __IGB_DOWN is the key to this design.
> 
> If watchdog_task runs *before* __IGB_DOWN is set, then the
> timer is stopped (by this patch) as required.
> 
> However, if watchdog_task runs *after* __IGB_DOWN is set,
> then the timer will not even be started (by watchdog_task).

Well, yes, but what if the two functions run *simultaneously* 
There is no mutual exclusion between these two pieces of code AFAICT