netdev - Re: [PATCH bpf-next v2 1/8] xdp: restructure redirect actions

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Message-ID: <559c6eb8-38b3-4719-2368-397f07daf5a5@intel.com>
Date:   Wed, 20 Jan 2021 18:26:23 +0100
From:   Björn Töpel <bjorn.topel@...el.com>
To:     Toke Høiland-Jørgensen <toke@...hat.com>,
        Björn Töpel <bjorn.topel@...il.com>,
        ast@...nel.org, daniel@...earbox.net, netdev@...r.kernel.org,
        bpf@...r.kernel.org
Cc:     magnus.karlsson@...el.com, maciej.fijalkowski@...el.com,
        kuba@...nel.org, jonathan.lemon@...il.com, maximmi@...dia.com,
        davem@...emloft.net, hawk@...nel.org, john.fastabend@...il.com,
        ciara.loftus@...el.com, weqaar.a.janjua@...el.com
Subject: Re: [PATCH bpf-next v2 1/8] xdp: restructure redirect actions

On 2021-01-20 17:30, Toke Høiland-Jørgensen wrote:
> Björn Töpel <bjorn.topel@...el.com> writes:
> 
[...]
>>
>> It can't be free'd but, ri->map can be cleared via
>> bpf_clear_redirect_map(). So, between the helper (setting) and the
>> tracepoint in xdp_do_redirect() it can be cleared (say if the XDP
>> program is swapped out, prior running xdp_do_redirect()).
> 
> But xdp_do_redirect() should be called on driver flush before exiting
> the NAPI cycle, so how can the XDP program be swapped out?
> 

To clarify; xdp_do_redirect() is called for each packet in the NAPI poll 
loop.

Yeah, you're right. The xdp_do_redirect() is within the RCU scope, so
the program wont be destroyed (but can be swapped though!).

Hmm, so IOW the bpf_clear_redirect_map() is not needed anymore...


Björn

[...]