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

From: Jakub Sitnicki <[email-masked]>
Date: Tue, 20 Jul 2021 12:27:22 +0200

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 <[email-masked]>
> ---

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).