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: <20201223124315.27451932@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Wed, 23 Dec 2020 12:43:15 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Antoine Tenart <atenart@...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

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.