Date: Wed, 12 Oct 2016 10:18:18 +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: <f1d9e34e-3d85-bd02-e660-6d647e4343fb@freebsd.org> In-Reply-To: <20161011121145.GJ6177@zxy.spb.ru> References: <20160928115909.GC54003@zxy.spb.ru> <a0425aad-a421-05bc-c1a8-c6fe06b83833@freebsd.org> <20161006111043.GH54003@zxy.spb.ru> <1431484c-c00e-24c5-bd76-714be8ae5ed5@freebsd.org> <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>
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This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --lo6WsNmCMpKpkEu6WS6lHh4jDTQdQVNts Content-Type: multipart/mixed; boundary="LWk23kBf77cRBBkv9C82XIU038BlJnf1A"; protected-headers="v1" 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: <f1d9e34e-3d85-bd02-e660-6d647e4343fb@freebsd.org> Subject: Re: 11.0 stuck on high network load References: <20160928115909.GC54003@zxy.spb.ru> <a0425aad-a421-05bc-c1a8-c6fe06b83833@freebsd.org> <20161006111043.GH54003@zxy.spb.ru> <1431484c-c00e-24c5-bd76-714be8ae5ed5@freebsd.org> <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> In-Reply-To: <20161011121145.GJ6177@zxy.spb.ru> --LWk23kBf77cRBBkv9C82XIU038BlJnf1A Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable Hi Slawa, On 10/11/16 2:11 PM, Slawa Olhovchenkov wrote: > On Tue, Oct 11, 2016 at 09:20:17AM +0200, Julien Charbon wrote: >> Then threads are competing for the INP_WLOCK lock. For the example, >> let's say the thread A wants to run tcp_input()/in_pcblookup_mbuf() an= d >> racing for this INP_WLOCK: >> >> https://github.com/freebsd/freebsd/blob/release/11.0.0/sys/netinet/in_= pcb.c#L1964 >> >> And thread B wants to run tcp_timer_2msl()/tcp_close()/in_pcbdrop() a= nd >> racing for this INP_WLOCK: >> >> https://github.com/freebsd/freebsd/blob/release/11.0.0/sys/netinet/tcp= _timer.c#L323 >> >> That leads to two cases: >> >> o Thread A wins the race: >> >> Thread A will continue tcp_input() as usal and INP_DROPPED flags is >> not set and inp is still in TCP hash table. >> Thread B is waiting on thread A to release INP_WLOCK after finishing= >> tcp_input() processing, and thread B will continue >> tcp_timer_2msl()/tcp_close()/in_pcbdrop() processing. >> >> o Thread B wins the race: >> >> Thread B runs tcp_timer_2msl()/tcp_close()/in_pcbdrop() and inp >> INP_DROPPED is set and inp being removed from TCP hash table. >> In parallel, thread A has found the inp in TCP hash before is was >> removed, and waiting on the found inp INP_WLOCK lock. >> Once thread B has released the INP_WLOCK lock, thread A gets this lo= ck >> and sees the INP_DROPPED flag and do "goto findpcb" but here because t= he >> inp is not more in TCP hash table and it will not be find again by >> in_pcblookup_mbuf(). >> >> Hopefully I am clear enough here. >=20 > Thanks, very clear. > Small qeustion: when both thread run on same CPU core, INP_WLOCK will > be re-schedule? Hmm, a thread can re-scheduled but not a lock. Thus no sure I understand your question here. :) > 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_tws= tart() 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. >=20 > 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. >=20 > 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? >=20 > 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(). -- Julien --LWk23kBf77cRBBkv9C82XIU038BlJnf1A-- --lo6WsNmCMpKpkEu6WS6lHh4jDTQdQVNts Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQEcBAEBCgAGBQJX/fHPAAoJEKVlQ5Je6dhxftQIAOFpZ+iF1ve1hfyXLFdI7kSx 2WU04gzNQ40+NXmMJvdZ3hQovwNbXCAu3aM7rqHbOV016Nf8x23gBFTqH+5wgE4z VRrfWifZZk8k1UFXsx2c6u2iVAcfx4WqDnJg98EtYP0Nh6dRuKuqcvPlblchHQJy OO4Zxc8TmIASZrOy1ce8m/fBspLkshoh7c1UdLtXlpyMyboh9dA/B+hC3lN2tVf8 7ghELfaPletstCfTQh6emgxE+IBEBbjAkgChsTCTmCMDoCK4jQ5YtbdjGJ8ZfSLi vBciJ7jWZhRHlANW8ZHbydHXvkOBVCPakmvt+xa8NotQhUSzB4UKRFgZG9Cw9tM= =OisL -----END PGP SIGNATURE----- --lo6WsNmCMpKpkEu6WS6lHh4jDTQdQVNts--
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