netdev - Re: Crash when receiving FIN-ACK in TCP_FIN

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Date:   Sat, 30 Nov 2019 02:51:19 +0000
From:   subashab@...eaurora.org
To:     Eric Dumazet <eric.dumazet@...il.com>,
        Josh Hunt <johunt@...mai.com>
Cc:     Neal Cardwell <ncardwell@...gle.com>,
        Netdev <netdev@...r.kernel.org>,
        Yuchung Cheng <ycheng@...gle.com>
Subject: Re: Crash when receiving FIN-ACK in TCP_FIN_WAIT1 state

>>> Since tcp_write_queue_purge() calls tcp_rtx_queue_purge() and we're 
>>> deleting everything in the retrans queue there, doesn't it make sense 
>>> to zero out all of those associated counters? Obviously clearing 
>>> sacked_out is helping here, but is there a reason to keep track of 
>>> lost_out, retrans_out, etc if retrans queue is now empty? Maybe 
>>> calling tcp_clear_retrans() from tcp_rtx_queue_purge() ?
>> 
>> First, I would like to understand if we hit this problem on current 
>> upstream kernels.
>> 
>> Maybe a backport forgot a dependency.
>> 
>> tcp_write_queue_purge() calls tcp_clear_all_retrans_hints(), not 
>> tcp_clear_retrans(),
>> this is probably for a reason.
>> 
>> Brute force clearing these fields might hide a serious bug.
>> 
> 
> I guess we are all too busy to get more understanding on this :/

Our test devices are on 4.19.x and it is not possible to switch to a 
newer
version. Perhaps Josh has seen this on a newer kernel.