netdev - Re: [PATCH net] vxlan: test dev->flags & IFF_UP before calling netif

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Date:   Thu, 7 Feb 2019 12:34:03 -0800
From:   Eric Dumazet <edumazet@...gle.com>
To:     "David S . Miller" <davem@...emloft.net>
Cc:     netdev <netdev@...r.kernel.org>,
        Eric Dumazet <eric.dumazet@...il.com>,
        Petr Machata <petrm@...lanox.com>,
        Ido Schimmel <idosch@...lanox.com>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        Stefano Brivio <sbrivio@...hat.com>
Subject: Re: [PATCH net] vxlan: test dev->flags & IFF_UP before calling netif_rx()

On Thu, Feb 7, 2019 at 12:27 PM Eric Dumazet <edumazet@...gle.com> wrote:
>
> netif_rx() must be called under a strict contract.
>
> At device dismantle phase, core networking clears IFF_UP
> and flush_all_backlogs() is called after rcu grace period
> to make sure no incoming packet might be in a cpu backlog
> and still referencing the device.
>
> Most drivers call netif_rx() from their interrupt handler,
> and since the interrupts are disabled at device dismantle,
> netif_rx() does not have to check dev->flags & IFF_UP
>
> Virtual drivers do not have this guarantee, and must
> therefore make the check themselves.

Since other netif_rx() callers seem to have the same issue, I wonder
if we simply could add a generic check.

Most high performance drivers no longer call netif_rx() so an extra check
in it wont be a problem.