Re: [PATCH net] iavf: Do not restart Tx queues after reset task failure

From: Leon Romanovsky <leon@kernel.org>
To: "Keller, Jacob E" <jacob.e.keller@intel.com>
Cc: ivecera <ivecera@redhat.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"sassmann@redhat.com" <sassmann@redhat.com>,
	"Piotrowski, Patryk" <patryk.piotrowski@intel.com>,
	SlawomirX Laba <slawomirx.laba@intel.com>,
	"Brandeburg, Jesse" <jesse.brandeburg@intel.com>,
	"Nguyen, Anthony L" <anthony.l.nguyen@intel.com>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	"moderated list:INTEL ETHERNET DRIVERS" 
	<intel-wired-lan@lists.osuosl.org>,
	open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net] iavf: Do not restart Tx queues after reset task failure
Date: Thu, 10 Nov 2022 11:17:09 +0200	[thread overview]
Message-ID: <Y2zBlcpKZooaQhtL@unreal> (raw)
In-Reply-To: <CO1PR11MB508996B0D00B5FE6187AF085D63E9@CO1PR11MB5089.namprd11.prod.outlook.com>

On Wed, Nov 09, 2022 at 08:11:55PM +0000, Keller, Jacob E wrote:
> 
> 
> > -----Original Message-----
> > From: Leon Romanovsky <leon@kernel.org>
> > Sent: Wednesday, November 9, 2022 10:21 AM
> > To: ivecera <ivecera@redhat.com>
> > Cc: netdev@vger.kernel.org; sassmann@redhat.com; Keller, Jacob E
> > <jacob.e.keller@intel.com>; Piotrowski, Patryk <patryk.piotrowski@intel.com>;
> > SlawomirX Laba <slawomirx.laba@intel.com>; Brandeburg, Jesse
> > <jesse.brandeburg@intel.com>; Nguyen, Anthony L
> > <anthony.l.nguyen@intel.com>; David S. Miller <davem@davemloft.net>; Eric
> > Dumazet <edumazet@google.com>; Jakub Kicinski <kuba@kernel.org>; Paolo
> > Abeni <pabeni@redhat.com>; moderated list:INTEL ETHERNET DRIVERS <intel-
> > wired-lan@lists.osuosl.org>; open list <linux-kernel@vger.kernel.org>
> > Subject: Re: [PATCH net] iavf: Do not restart Tx queues after reset task failure
> > 
> > On Tue, Nov 08, 2022 at 11:25:02AM +0100, Ivan Vecera wrote:
> > > After commit aa626da947e9 ("iavf: Detach device during reset task")
> > > the device is detached during reset task and re-attached at its end.
> > > The problem occurs when reset task fails because Tx queues are
> > > restarted during device re-attach and this leads later to a crash.
> > 
> > <...>
> > 
> > > +	if (netif_running(netdev)) {
> > > +		/* Close device to ensure that Tx queues will not be started
> > > +		 * during netif_device_attach() at the end of the reset task.
> > > +		 */
> > > +		rtnl_lock();
> > > +		dev_close(netdev);
> > > +		rtnl_unlock();
> > > +	}
> > 
> > Sorry for my naive question, I see this pattern a lot (including RDMA),
> > so curious. Everyone checks netif_running() outside of rtnl_lock, while
> > dev_close() changes state bit __LINK_STATE_START. Shouldn't rtnl_lock()
> > placed before netif_running()?
> 
> Yes I think you're right. A ton of people check it without the lock but I think thats not strictly safe. Is dev_close safe to call when netif_running is false? Why not just remove the check and always call dev_close then.

I honestly don't know.

To remove any doubts, this patch is LGTM.

Thanks,
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>