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:   Tue, 22 Dec 2020 10:21:19 +0100
From:   Antoine Tenart <atenart@...nel.org>
To:     Alexander Duyck <alexander.duyck@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        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

Hello Alexander, Jakub,

Quoting Alexander Duyck (2020-12-22 00:21:57)
> 
> Looking over this patch it seems kind of obvious that extending the
> xps_map_mutex is making things far more complex then they need to be.
> 
> Applying the rtnl_mutex would probably be much simpler. Although as I
> think you have already discovered we need to apply it to the store,
> and show for this interface. In addition we probably need to perform
> similar locking around traffic_class_show in order to prevent it from
> generating a similar error.

I don't think we have the same kind of issues with traffic_class_show:
dev->num_tc is used, but not for navigating through the map. Protecting
only a single read wouldn't change much. We can still think about what
could go wrong here without the lock, but that is not related to this
series of fixes.

If I understood correctly, as things are a bit too complex now, you
would prefer that we go for the solution proposed in v1?

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.

Jakub, should I send a v3 then?

Thanks!
Antoine