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

From: Jakub Kicinski <kuba@kernel.org>
To: Leon Romanovsky <leon@kernel.org>
Cc: Ivan Vecera <ivecera@redhat.com>,
	SlawomirX Laba <slawomirx.laba@intel.com>,
	Eric Dumazet <edumazet@google.com>,
	"netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"Piotrowski, Patryk" <patryk.piotrowski@intel.com>,
	Paolo Abeni <pabeni@redhat.com>,
	"moderated list:INTEL ETHERNET DRIVERS\"
	<intel-wired-lan@lists.osuosl.org>,
	open list <linux-kernel@vger.kernel.org>"@osuosl.org,
	"David S. Miller" <davem@davemloft.net>,
	"sassmann@redhat.com" <sassmann@redhat.com>
Subject: Re: [Intel-wired-lan] [PATCH net] iavf: Do not restart Tx queues after reset task failure
Date: Thu, 10 Nov 2022 12:24:18 -0800	[thread overview]
Message-ID: <20221110122418.32414666@kernel.org> (raw)
In-Reply-To: <Y20vtqd6raqg8iwy@unreal>

On Thu, 10 Nov 2022 19:07:02 +0200 Leon Romanovsky wrote:
> > > 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.
> > 
> > Check for a bit value (like netif_runnning()) is much cheaper than
> > unconditionally taking global lock like RTNL.  
> 
> This cheap operation is racy and performed in non-performance
> critical path.

To be clear - the rtnl_lock around the entire if is still racy 
in the grand scheme of things, no? What's stopping someone from
bringing the device right back up after you drop the lock?
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