netdev - Re: [PATCH net] tcp: handle inet_csk_reqsk_queue

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Date:   Fri, 8 Mar 2019 23:40:24 +0100
From:   Guillaume Nault <gnault@...hat.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: handle inet_csk_reqsk_queue_add() failures

On Fri, Mar 08, 2019 at 02:34:07PM -0800, Eric Dumazet wrote:
> 
> 
> On 03/08/2019 02:22 PM, Guillaume Nault wrote:
> > On Fri, Mar 08, 2019 at 01:33:02PM -0800, Eric Dumazet wrote:
> >>
> >>
> >> On 03/08/2019 01:09 PM, Guillaume Nault wrote:
> >>> @@ -216,7 +216,12 @@ struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
> >>>  		refcount_set(&req->rsk_refcnt, 1);
> >>>  		tcp_sk(child)->tsoffset = tsoff;
> >>>  		sock_rps_save_rxhash(child, skb);
> >>> -		inet_csk_reqsk_queue_add(sk, req, child);
> >>> +		if (!inet_csk_reqsk_queue_add(sk, req, child)) {
> >>> +			bh_unlock_sock(child);
> >>> +			sock_put(child);
> >>> +			child = NULL;
> >>> +			reqsk_put(req);
> >>
> >> Since we use reqsk_free(req) in the same function, we can use reqsk_free(req)
> >> here as well ?
> >>
> > That was my first approach, but reqsk_free() doesn't like it:
> > 
> > static inline void reqsk_free(struct request_sock *req)
> > {
> >         /* temporary debugging */
> > 	WARN_ON_ONCE(refcount_read(&req->rsk_refcnt) != 0);
> > ...
> > }
> 
> Oh right, there is this refcount_set(&req->rsk_refcnt, 1) before the call
> to inet_csk_reqsk_queue_add(sk, req, child);
> 
> So just change the TFO case only :)
> 
Well.. refcount is 1 in the TFO case too.

Long term, do we want to keep the WARN_ON_ONCE()? If so, we should
probably remove the comment.