Messages in this thread | | | From | Eric Dumazet <> | Date | Thu, 8 Jun 2023 13:54:09 +0200 | Subject | Re: [PATCH v2] tcp: fix connection reset due to tw hashdance race. |
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On Thu, Jun 8, 2023 at 1:24 PM Duan,Muquan <duanmuquan@baidu.com> wrote: > > Besides trying to find the right tw sock, another idea is that if FIN segment finds listener sock, just discard the segment, because this is obvious a bad case, and the peer will retransmit it. Or for FIN segment we only look up in the established hash table, if not found then discard it. >
Sure, please give the RFC number and section number that discusses this point, and then we might consider this.
Just another reminder about TW : timewait sockets are "best effort".
Their allocation can fail, and /proc/sys/net/ipv4/tcp_max_tw_buckets can control their number to 0
Applications must be able to recover gracefully if a 4-tuple is reused too fast.
> > 2023年6月8日 下午12:13,Eric Dumazet <edumazet@google.com> 写道: > > On Thu, Jun 8, 2023 at 5:59 AM Duan,Muquan <duanmuquan@baidu.com> wrote: > > > Hi, Eric, > > Thanks a lot for your explanation! > > Even if we add reader lock, if set the refcnt outside spin_lock()/spin_unlock(), during the interval between spin_unlock() and refcnt_set(), other cpus will see the tw sock with refcont 0, and validation for refcnt will fail. > > A suggestion, before the tw sock is added into ehash table, it has been already used by tw timer and bhash chain, we can firstly add refcnt to 2 before adding two to ehash table,. or add the refcnt one by one for timer, bhash and ehash. This can avoid the refcont validation failure on other cpus. > > This can reduce the frequency of the connection reset issue from 20 min to 180 min for our product, We may wait quite a long time before the best solution is ready, if this obvious defect is fixed, userland applications can benefit from it. > > Looking forward to your opinions! > > > Again, my opinion is that we need a proper fix, not work arounds. > > I will work on this a bit later. > > In the meantime you can apply locally your patch if you feel this is > what you want. > >
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