Date: Wed, 12 Oct 2016 12:52:33 +0300 From: Slawa Olhovchenkov <slw@zxy.spb.ru> To: Julien Charbon <jch@freebsd.org> 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: <20161012095233.GC57714@zxy.spb.ru> In-Reply-To: <4b0d4b58-6d13-3cd5-6991-27163f27acca@freebsd.org> References: <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> <4b0d4b58-6d13-3cd5-6991-27163f27acca@freebsd.org>
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On Wed, Oct 12, 2016 at 11:42:38AM +0200, Julien Charbon wrote:
> On 10/12/16 11:29 AM, Slawa Olhovchenkov wrote:
> > On Wed, Oct 12, 2016 at 11:19:48AM +0200, Julien Charbon wrote:
> >
> >>> 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.
> >
> > Thanks, nice.
> >
> >>>>> 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_DROPPED
> >>>> 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 now
> >>>>> 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 independed
> >>>>> 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 &= ~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, some
> >> are only in TOE TCP stack.
> >
> > 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.
I am about case when at time of first INP_WUNLOCK() tcp_timer_2msl()
don't see INP_TIMEWAIT, call tcp_close(), tcp_close() do INP_WUNLOCK()
and now Chelsio TOE take INP_WLOCK, do tcp_twstart() and set
INP_TIMEWAIT. After this tcp_timer_2msl resume and have unexpected
INP_TIMEWAIT in tcp_usr_detach().
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