Date: Sat, 10 Apr 2021 14:19:05 +0200 From: tuexen@freebsd.org To: "Scheffenegger, Richard" <Richard.Scheffenegger@netapp.com> Cc: Rick Macklem <rmacklem@uoguelph.ca>, Youssef GHORBAL <youssef.ghorbal@pasteur.fr>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: NFS Mount Hangs Message-ID: <077ECE2B-A84C-440D-AAAB-00293C841F14@freebsd.org> In-Reply-To: <SN4PR0601MB3728AF2554FDDFB4EEF2C95B86729@SN4PR0601MB3728.namprd06.prod.outlook.com> References: <C643BB9C-6B61-4DAC-8CF9-CE04EA7292D0@tildenparkcapital.com> <3750001D-3F1C-4D9A-A9D9-98BCA6CA65A4@tildenparkcapital.com> <33693DE3-7FF8-4FAB-9A75-75576B88A566@tildenparkcapital.com> <D67AF317-D238-4EC0-8C7F-22D54AD5144C@pasteur.fr> <YQXPR0101MB09684AB7BEFA911213604467DD669@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <C87066D3-BBF1-44E1-8398-E4EB6903B0F2@tildenparkcapital.com> <8E745920-1092-4312-B251-B49D11FE8028@pasteur.fr> <YQXPR0101MB0968C44C7C82A3EB64F384D0DD7B9@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <DEF8564D-0FE9-4C2C-9F3B-9BCDD423377C@freebsd.org> <YQXPR0101MB0968E0A17D8BCACFAF132225DD7A9@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <SN4PR0601MB3728E392BCA494EAD49605FE86789@SN4PR0601MB3728.namprd06.prod.outlook.com> <YQXPR0101MB09686B4F921B96DCAFEBF874DD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <765CE1CD-6AAB-4BEF-97C6-C2A1F0FF4AC5@freebsd.org> <YQXPR0101MB096876B44F33BAD8991B62C8DD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <2B189169-C0C9-4DE6-A01A-BE916F10BABA@freebsd.org> <YQXPR0101MB09688645194907BBAA6E7C7ADD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <BF5D23D3-5DBD-4E29-9C6B-F4CCDC205353@freebsd.org> <YQXPR0101MB096826445C85921C8F6410A2DD779@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <E4A51EAD-8F9A-49BB-8852-F9D61BDD9EA4@freebsd.org> <YQXPR0101MB09682F230F25FBF3BC427135DD729@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <SN4PR0601MB3728AF2554FDDFB4EEF2C95B86729@SN4PR0601MB3728.namprd06.prod.outlook.com>
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> On 10. Apr 2021, at 11:19, Scheffenegger, Richard = <Richard.Scheffenegger@netapp.com> wrote: >=20 > Hi Rick, >=20 >> Well, I have some good news and some bad news (the bad is mostly for = Richard). >>=20 >> The only message logged is: >> tcpflags 0x4<RST>; tcp_do_segment: Timestamp missing, segment = processed normally >>=20 >> But...the RST battle no longer occurs. Just one RST that works and = then the SYN gets SYN,ACK'd by the FreeBSD end and off it goes... >>=20 >> So, what is different? >>=20 >> r367492 is reverted from the FreeBSD server. >> I did the revert because I think it might be what otis@ hang is being = caused by. (In his case, the Recv-Q grows on the socket for the stuck = Linux client, while others work. >>=20 >> Why does reverting fix this? >> My only guess is that the krpc gets the upcall right away and sees a = EPIPE when it does soreceive()->results in soshutdown(SHUT_WR). >=20 > With r367492 you don't get the upcall with the same error state? Or = you don't get an error on a write() call, when there should be one? My understanding is that he needs this error indication when calling = shutdown(). >=20 > =46rom what you describe, this is on writes, isn't it? (I'm asking, at = the original problem that was fixed with r367492, occurs in the read = path (draining of ths so_rcv buffer in the upcall right away, which = subsequently influences the ACK sent by the stack). >=20 > I only added the so_snd buffer after some discussion, if the WAKESOR = shouldn't have a symmetric equivalent on WAKESOW.... >=20 > Thus a partial backout (leaving the WAKESOR part inside, but reverting = the WAKESOW part) would still fix my initial problem about erraneous = DSACKs (which can also lead to extremely poor performance with Linux = clients), but possible address this issue... >=20 > Can you perhaps take MAIN and apply https://reviews.freebsd.org/D29690 = for the revert only on the so_snd upcall? Since the release of 13.0 is almost done, can we try to fix the issue = instead of reverting the commit? >=20 > If this doesn't help, some major surgery will be necessary to prevent = NFS sessions with SACK enabled, to transmit DSACKs... My understanding is that the problem is related to getting a local error = indication after receiving a RST segment too late or not at all. Best regards Michael >=20 >=20 >> I know from a printf that this happened, but whether it caused the = RST battle to not happen, I don't know. >>=20 >> I can put r367492 back in and do more testing if you'd like, but I = think it probably needs to be reverted? >=20 > Please, I don't quite understand why the exact timing of the upcall = would be that critical here... >=20 > A comparison of the soxxx calls and errors between the "good" and the = "bad" would be perfect. I don't know if this is easy to do though, as = these calls appear to be scattered all around the RPC / NFS source = paths. >=20 >> This does not explain the original hung Linux client problem, but = does shed light on the RST war I could create by doing a network = partitioning. >>=20 >> rick >=20 > _______________________________________________ > freebsd-net@freebsd.org mailing list > https://lists.freebsd.org/mailman/listinfo/freebsd-net > To unsubscribe, send any mail to "freebsd-net-unsubscribe@freebsd.org"
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