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

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Message-ID: <Y20vtqd6raqg8iwy@unreal>
Date:   Thu, 10 Nov 2022 19:07:02 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Ivan Vecera <ivecera@...hat.com>
Cc:     "Keller, Jacob E" <jacob.e.keller@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "sassmann@...hat.com" <sassmann@...hat.com>,
        "Piotrowski, Patryk" <patryk.piotrowski@...el.com>,
        SlawomirX Laba <slawomirx.laba@...el.com>,
        "Brandeburg, Jesse" <jesse.brandeburg@...el.com>,
        "Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "moderated list:INTEL ETHERNET DRIVERS" 
        <intel-wired-lan@...ts.osuosl.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net] iavf: Do not restart Tx queues after reset task
 failure

On Thu, Nov 10, 2022 at 03:51:47PM +0100, Ivan Vecera wrote:
> On Wed, 9 Nov 2022 20:11:55 +0000
> "Keller, Jacob E" <jacob.e.keller@...el.com> wrote:
> 
> > > 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.
> > 
> > Thanks,
> > Jake
> 
> 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.

Thanks

> 
> Ivan
>