netdev - Re: [PATCH bpf 1/3] bpf, sockmap: zap ingress queues after stopping strparser

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Message-ID: <87v955qnzp.fsf@cloudflare.com>
Date:   Tue, 20 Jul 2021 12:27:22 +0200
From:   Jakub Sitnicki <jakub@...udflare.com>
To:     John Fastabend <john.fastabend@...il.com>
Cc:     daniel@...earbox.net, xiyou.wangcong@...il.com,
        alexei.starovoitov@...il.com, bpf@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf 1/3] bpf, sockmap: zap ingress queues after stopping
 strparser

On Mon, Jul 19, 2021 at 11:48 PM CEST, John Fastabend wrote:
> We don't want strparser to run and pass skbs into skmsg handlers when
> the psock is null. We just sk_drop them in this case. When removing
> a live socket from map it means extra drops that we do not need to
> incur. Move the zap below strparser close to avoid this condition.
>
> This way we stop the stream parser first stopping it from processing
> packets and then delete the psock.
>
> Fixes: a136678c0bdbb ("bpf: sk_msg, zap ingress queue on psock down")
> Signed-off-by: John Fastabend <john.fastabend@...il.com>
> ---

To confirm my understanding - the extra drops can happen because
currently we are racing to clear SK_PSOCK_TX_ENABLED flag in
sk_psock_drop with sk_psock_verdict_apply, which checks the flag before
pushing skb onto psock->ingress_skb queue (or possibly straight into
psock->ingress_msg queue on no redirect).