Date: Wed, 12 Oct 2016 11:42:38 +0200 From: Julien Charbon <jch@freebsd.org> To: Slawa Olhovchenkov <slw@zxy.spb.ru> Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-stable@FreeBSD.org, hiren panchasara <hiren@strugglingcoder.info> Subject: Re: 11.0 stuck on high network load Message-ID: <4b0d4b58-6d13-3cd5-6991-27163f27acca@freebsd.org> In-Reply-To: <20161012092945.GB57714@zxy.spb.ru> References: <20161010133220.GU54003@zxy.spb.ru> <23f1200e-383e-befb-b76d-c88b3e1287b0@freebsd.org> <20161010142941.GV54003@zxy.spb.ru> <52d634aa-639c-bef7-1f10-c46dbadc4d85@freebsd.org> <20161010173531.GI6177@zxy.spb.ru> <8143cd8f-c007-2378-b004-b2b037402d03@freebsd.org> <20161011121145.GJ6177@zxy.spb.ru> <f1d9e34e-3d85-bd02-e660-6d647e4343fb@freebsd.org> <20161012084045.GA57714@zxy.spb.ru> <f3c0e73a-5e6e-2190-aed3-499250c1764c@freebsd.org> <20161012092945.GB57714@zxy.spb.ru>
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From: Julien Charbon <jch@freebsd.org>
To: Slawa Olhovchenkov <slw@zxy.spb.ru>
Cc: Konstantin Belousov <kostikbel@gmail.com>, freebsd-stable@FreeBSD.org,
hiren panchasara <hiren@strugglingcoder.info>
Message-ID: <4b0d4b58-6d13-3cd5-6991-27163f27acca@freebsd.org>
Subject: Re: 11.0 stuck on high network load
References: <20161010133220.GU54003@zxy.spb.ru>
<23f1200e-383e-befb-b76d-c88b3e1287b0@freebsd.org>
<20161010142941.GV54003@zxy.spb.ru>
<52d634aa-639c-bef7-1f10-c46dbadc4d85@freebsd.org>
<20161010173531.GI6177@zxy.spb.ru>
<8143cd8f-c007-2378-b004-b2b037402d03@freebsd.org>
<20161011121145.GJ6177@zxy.spb.ru>
<f1d9e34e-3d85-bd02-e660-6d647e4343fb@freebsd.org>
<20161012084045.GA57714@zxy.spb.ru>
<f3c0e73a-5e6e-2190-aed3-499250c1764c@freebsd.org>
<20161012092945.GB57714@zxy.spb.ru>
In-Reply-To: <20161012092945.GB57714@zxy.spb.ru>
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On 10/12/16 11:29 AM, Slawa Olhovchenkov wrote:
> On Wed, Oct 12, 2016 at 11:19:48AM +0200, Julien Charbon wrote:
>=20
>>> if INP_WLOCK is like spinlock -- this is dead lock.
>>> if INP_WLOCK is like mutex -- thread1 resheduled.
>>
>> Thanks, I understand you question now. No an interrupt cannot bypass=
a
>> lock: Here INP_WLOCK is like mutex -- thread1 resheduled.
>=20
> Thanks, nice.
>=20
>>>>> As I remeber race created by call tcp_twstart() at time of end
>>>>> tcp_close(), at path sofree()-tcp_usr_detach() and unexpected
>>>>> INP_TIMEWAIT state in the tcp_usr_detach(). INP_TIMEWAIT set in tcp=
_twstart()
>>>>
>>>> Exactly, thus the current fix is: If you already have the INP_DROP=
PED
>>>> flag set you are not allowed to call tcp_twstart(), actually it is a=
>>>> good candidate for a new INVARIANT. Let me add that.
>>>>
>>>>> After check source code I am found invocation of tcp_twstart() in
>>>>> sys/netinet/tcp_stacks/fastpath.c, sys/netinet/tcp_input.c,
>>>>> sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c, sys/dev/cxgbe/tom/t4_cpl_io.c.
>>>>>
>>>>> Invocation from sys/netinet/tcp_stacks/fastpath.c and
>>>>> sys/netinet/tcp_input.c guarded by INP_WLOCK in tcp_input(), and no=
w
>>>>> will be OK.
>>>>>
>>>>> Invocation from sys/dev/cxgb/ulp/tom/cxgb_cpl_io.c and
>>>>> sys/dev/cxgbe/tom/t4_cpl_io.c is not clear to me, I am see independ=
ed
>>>>> INP_WLOCK. Is this OK?
>>>>>
>>>>> Can be thread A wants do_peer_close() directed from chelsio IRQ
>>>>> handler, bypass tcp_input()?
>>>>
>>>> If you look carefully INP_WLOCK is used in cxgb_cpl_io.c and
>>>> t4_cpl_io.c before calling tcp_twstart().
>>>
>>> Yes, and you remeber: sys/netinet/tcp_subr.c
>>>
>>> 1535 struct tcpcb *
>>> 1536 tcp_close(struct tcpcb *tp)
>>> 1537 {
>>> ...
>>> 1569 INP_WUNLOCK(inp);
>>> 1570 ACCEPT_LOCK();
>>> 1571 SOCK_LOCK(so);
>>> 1572 so->so_state &=3D ~SS_PROTOREF;
>>> 1573 sofree(so);
>>> 1574 return (NULL);
>>>
>>> sofree() call tcp_usr_detach() and in tcp_usr_detach() we have
>>> unexpected INP_TIMEWAIT.
>>
>> I see, thus just for the context: The TCP stack in sys/dev/cxgb* is =
a
>> TOE (TCP Offload Engine?) TCP stack for Chelsio NICs, it is a
>> separate/side TCP stack that is used only with TCP_OFFLOAD option.
>>
>> This TOE TCP stack actually has its own set of detach()/input()
>> functions and seems to check INP_DROPPED flag properly. I guess @np
>> check fixes in socket TCP stack and decides which one can also impact
>> the Chelsio TOE TCP stack. Some bugs are only in socket TCP stack, so=
me
>> are only in TOE TCP stack.
>=20
> I am fear about other direction -- setting INP_TIMEWAIT in Chelsio TOE
> TCP stack and impact this to
> tcp_timer_2msl()/tcp_close()/sofree()/tcp_usr_detach() path.
I see, I expect no problem on this side as tcp_timer_2msl() checks the
INP_TIMEWAIT flag and do not call tcp_close() if set.
--
Julien
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