netdev - RE: [Intel-wired-lan] [PATCH iwl-net v2] iavf: fix circular lock dependency with netdev

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Message-ID: <SJ0PR11MB58659496CF5E4D27CAB5D46D8FC42@SJ0PR11MB5865.namprd11.prod.outlook.com>
Date: Thu, 20 Feb 2025 09:22:01 +0000
From: "Romanowski, Rafal" <rafal.romanowski@...el.com>
To: Jakub Kicinski <kuba@...nel.org>, "Keller, Jacob E"
	<jacob.e.keller@...el.com>
CC: Intel Wired LAN <intel-wired-lan@...ts.osuosl.org>, netdev
	<netdev@...r.kernel.org>, "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
	"Kitszel, Przemyslaw" <przemyslaw.kitszel@...el.com>
Subject: RE: [Intel-wired-lan] [PATCH iwl-net v2] iavf: fix circular lock
 dependency with netdev_lock

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of Jakub
> Kicinski
> Sent: Friday, February 14, 2025 8:40 PM
> To: Keller, Jacob E <jacob.e.keller@...el.com>
> Cc: Intel Wired LAN <intel-wired-lan@...ts.osuosl.org>; netdev
> <netdev@...r.kernel.org>; Nguyen, Anthony L <anthony.l.nguyen@...el.com>;
> Kitszel, Przemyslaw <przemyslaw.kitszel@...el.com>
> Subject: Re: [Intel-wired-lan] [PATCH iwl-net v2] iavf: fix circular lock dependency
> with netdev_lock
> 
> On Thu, 13 Feb 2025 16:30:59 -0800 Jacob Keller wrote:
> > Analyzing the places where we take crit_lock in the driver there are
> > two
> > sources:
> >
> > a) several of the work queue tasks including adminq_task,
> > watchdog_task, reset_task, and the finish_config task.
> >
> > b) various callbacks which ultimately stem back to .ndo operations or
> > ethtool operations.
> >
> > The latter cannot be triggered until after the netdevice registration
> > is completed successfully.
> >
> > The iAVF driver uses alloc_ordered_workqueue, which is an unbound
> > workqueue that has a max limit of 1, and thus guarantees that only a
> > single work item on the queue is executing at any given time, so none
> > of the other work threads could be executing due to the ordered workqueue
> guarantees.
> >
> > The iavf_finish_config() function also does not do anything else after
> > register_netdevice, unless it fails. It seems unlikely that the driver
> > private crit_lock is protecting anything that register_netdevice()
> > itself touches.
> >
> > Thus, to fix this ABBA lock violation, lets simply release the
> > adapter->crit_lock as well as netdev_lock prior to calling
> > register_netdevice(). We do still keep holding the RTNL lock as
> > required by the function. If we do fail to register the netdevice,
> > then we re-acquire the adapter critical lock to finish the transition
> > back to __IAVF_INIT_CONFIG_ADAPTER.
> >
> > This ensures every call where both netdev_lock and the
> > adapter->crit_lock are acquired under the same ordering.
> 
> Thanks a lot for figuring this out, much appreciated!
> 
> Reviewed-by: Jakub Kicinski <kuba@...nel.org>


Tested-by: Rafal Romanowski <rafal.romanowski@...el.com>