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

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Date:   Fri, 8 Mar 2019 15:47:25 -0800
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Guillaume Nault <gnault@...hat.com>,
        Eric Dumazet <eric.dumazet@...il.com>
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net] tcp: handle inet_csk_reqsk_queue_add() failures



On 03/08/2019 02:40 PM, Guillaume Nault wrote:
> 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.


Arg...

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

We want to keep the warning.

We do not have a way to tell if the req was ever inserted in a hash table, so better play safe.

Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Thanks !