netdev - Re: [PATCH net v2 1/3] net: fix race conditions in xps by locking the maps and dev->tc

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Message-ID: <160875701664.1783433.16072409555972227523@kwain.local>
Date:   Wed, 23 Dec 2020 21:56:56 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        David Miller <davem@...emloft.net>,
        Netdev <netdev@...r.kernel.org>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net v2 1/3] net: fix race conditions in xps by locking the maps and dev->tc_num

Quoting Jakub Kicinski (2020-12-23 21:43:15)
> On Wed, 23 Dec 2020 21:35:15 +0100 Antoine Tenart wrote:
> > > > - For net-next, to resend patches 2 and 3 from v2 (they'll have to be
> > > >   slightly reworked, to take into account the review from Alexander and
> > > >   the rtnl lock). The patches can be sent once the ones for net land in
> > > >   net-next.  
> > > 
> > > If the direction is to remove xps_map_mutex, why would we need patch 2?
> > > 🤔  
> > 
> > Only the patches for net are needed to fix the race conditions.
> > 
> > In addition to use the xps_map mutex, patches 2 and 3 from v2 factorize
> > the code into a single function, as xps_cpus_show and xps_rxqs_show
> > share the same logic. That would improve maintainability, but isn't
> > mandatory.
> > 
> > Sorry, it was not very clear...
> 
> I like the cleanup, sorry I'm net very clear either.
> 
> My understanding was that patch 2 was only needed to have access to the
> XPS lock, if we don't plan to use that lock netif_show_xps_queue() can
> stay in the sysfs file, right? I'm all for the cleanup and code reuse
> for rxqs, I'm just making sure I'm not missing anything. I wasn't
> seeing a reason to move netif_show_xps_queue(), that's all.

You understood correctly, the only reason to move this code out of sysfs
was to access the xps_map lock. Without the need, the code can stay in
sysfs.

Patch 2 is not only moving the code out of sysfs, but also reworking
xps_cpus_show. I think I now see where the confusion comes from: the
reason patches 2 and 3 were in two different patches was because they
were targeting net and different kernel versions. They could be squashed
now.

Antoine