netdev - Re: [PATCH net-next] inet: Always increment refcount in inet_twsk

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Date:	Mon, 20 Jul 2015 19:14:35 -0000
From:	subashab@...eaurora.org
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] inet: Always increment refcount in
 inet_twsk_schedule

>> //Initialize time wait socket and setup timer
>> inet_twsk_alloc() tw_refcnt = 0
>> __inet_twsk_hashdance() tw_refcnt = 3
>> inet_twsk_schedule() tw_refcnt = 4
>> inet_twsk_put() tw_refcnt = 3
>>
>> //Receive packet 1 in timewait state
>> tcp_timewait_state_process() -> inet_twsk_schedule tw_refcnt = 3 (no
>> change)
>
> This is obviously wrong.
>
> If a timewait socket is found, do we increment its refcnt before
> proceeding.
We do not increment refcount currently when we find a timewait socket.

> I've received some private mails about tw issues, that turned to be
> caused by buggy drivers or buggy arch specific code.
>
> Are you crashed observed on x86 ?
>
This is observed on ARM devices. In the current debug, all time wait
socket refcount changes were happening in TCP stack only and there was no
platform / driver code involved.

According to my understanding, we would need to increment the time wait
socket refcount first before proceeding with any subsequent operations.
However, I request your expert opinion on this.


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