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

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Date:   Wed, 23 Dec 2020 21:35:15 +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 21:11:10)
> On Wed, 23 Dec 2020 20:36:33 +0100 Antoine Tenart wrote:
> > Quoting Jakub Kicinski (2020-12-23 19:27:29)
> > > On Tue, 22 Dec 2020 08:12:28 -0800 Alexander Duyck wrote:  
> > > > On Tue, Dec 22, 2020 at 1:21 AM Antoine Tenart <atenart@...nel.org> wrote:
> > > >   
> > > > > If I understood correctly, as things are a bit too complex now, you
> > > > > would prefer that we go for the solution proposed in v1?    
> > > > 
> > > > Yeah, that is what I am thinking. Basically we just need to make sure
> > > > the num_tc cannot be updated while we are reading the other values.  
> > > 
> > > Yeah, okay, as much as I dislike this approach 300 lines may be a little
> > > too large for stable.
> > >   
> > > > > I can still do the code factoring for the 2 sysfs show operations, but
> > > > > that would then target net-next and would be in a different series. So I
> > > > > believe we'll use the patches of v1, unmodified.    
> > > 
> > > Are you saying just patch 3 for net-next?  
> > 
> > The idea would be to:
> > 
> > - For net, to take all 4 patches from v1. If so, do I need to resend
> >   them?
> 
> Yes, please.

Will do.

> > - 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...

Antoine