linux-kernel - Re: [PATCH v2] igb: Fix watchdog

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Message-ID: <aEaAGqP-KtcYCMs-@50995b80b0f4>
Date: Mon, 9 Jun 2025 09:32:58 +0300
From: Ian Ray <ian.ray@...ealthcare.com>
To: Jakub Kicinski <kuba@...nel.org>
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 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).

Regards,
Ian