Olga Kornievskaia wrote: >On Tue, Apr 13, 2021 at 3:29 PM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: >> >> On Tue, Apr 13, 2021 at 02:59:27PM -0400, Olga Kornievskaia wrote: >> > On Tue, Apr 13, 2021 at 1:17 PM J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote: >> > > >> > > On Tue, Apr 13, 2021 at 09:31:37AM -0400, Olga Kornievskaia wrote: >> > > > On Tue, Apr 13, 2021 at 3:08 AM Rick Macklem <rmacklem@xxxxxxxxxxx> wrote: >> > > > > >> > > > > Hi, >> > > > > >> > > > > During testing of a Fedora Core 30 (5.2.10 kernel) against a FreeBSD >> > > > > server (4.1 mount), I have been simulating a network partitioning >> > > > > for a few minutes (until the TCP connection goes to SYN_SENT on >> > > > > the Linux client). >> > > > > >> > > > > Sometimes, after the network partition heals, the FreeBSD server >> > > > > replies NFS4ERR_SEQ_MISORDERED. >> > > > > Looking at the packet trace, the seqid for the slot has advanced by >> > > > > 2 instead of 1. An RPC request for old-seqid + 1 never seems to get >> > > > > sent. >> > > > > --> Since sending an RPC with "seqid + 2" but never sending one >> > > > > that is "seqid + 1" for a slot seems harmless, I have added an optional >> > > > > hack (can be turned off), to allow this case instead of replying >> > > > > NFS4ERR_SEQ_MISORDERED for it. The code will still reply >> > > > > NFS4ERR_SEQ_MISORDERED if an RPC for the slot with >> > > > > "old seqid + 1" in it. >> > > > > --> Yes, doing this hack is a violation of RFC5661, but I've >> > > > > done it anyhow. >> > > > > >> > > > > If you are interested in a packet capture with this in it: >> > > > > fetch https://people.freebsd.org/~rmacklem/linuxtofreenfs.pcap >> > > > > - then look at packet #1945 and #2072 >> > > > > --> You'll see that slot #1 seqid goes from 4 to 6. There is no >> > > > > slot#1 seqid 5 RPC sent on the wire. >> > > > > (This packet capture was taken on the Linux client using >> > > > > tcpdump.) >> > > > > --> Btw, the "RST battle" you'll see in the above trace between >> > > > > #2005 and #2068 that goes on until the FreeBSD >> > > > > krpc/NFS times out the connection after 6min. seems to be a recent >> > > > > FreeBSD TCP bug. >> > > > > I have reproduced this seqid advances by 2 on an older system >> > > > > that does not "RST battle" and allows the reconnect right away, >> > > > > once the network partition is healed, so it does seem to be >> > > > > relevant to this bug. >> > > > > >> > > > > Someday, I will get around to upgrading to a more recent Linux >> > > > > kernel and will test to see if I can still reproduce this bug. >> > > > > On 5.2.10, it is intermittent and does not occur every time I >> > > > > do the network partitioning test. >> > > > > >> > > > > Mostly just fyi, rick >> > > > >> > > > Hi Rick, >> > > > >> > > > I think this is happening because slotid=1 had something queued up >> > > > using seqid=5 and that was interrupted because the connection was >> > > > RSTed. For the interrupted slot, the client would send solo SEQUENCE >> > > > with +1 seqid. >> > > >> > > Doesn't the client send the solo SEQUENCE with seqid 5 in that case? >> > >> > No it sends with seq+1 because NFS layer client doesn't know if seqid >> > actually was actually transmitted before the connection got caught >> > (and/or received by the server). >> >> But then the MISORDERED tells the client it wasn't received, so the >> client follows up with a call with seqid 5--is that what happens? > >Correct. If there were no error then the server did indeed consume >seqid. And if an error was returned then the client knows to >decrement. Ok. Yes. I took a closer look at the packet capture and that is what happened. On slot#1...(server expecting seqid == 5): - Sequence with seqid 6 --> reply NFS4ERR_SEQ_MISORDERED - next use of slot#1, Sequence with seqid 5 --> reply NFS_OK - next use of slot#1, Sequence with seqid 6 --> reply NFS_OK - then slot#1 gets used normally by other RPCs So it's an intentional "probe to re-synchronize the seqid for the slot"? Clever. I'll back my "hack" out, since I now see it is not necessary (and does violate the RFC'-). So, is this how the Linux client deals with "soft,intr" NFSv4.1 mounts? --> I've never solved that for FreeBSD and just note in the BUGS section of the man page that "soft,intr" mount options break an NFSv4 mount. I might *borrow* this idea. I'll attribute it to whoever thought of the idea, if you let me know who that is? Thanks for the clarification, rick > Sorry, I seem to recall we went through this all a couple years ago, but > now I've forgotten how it works. > > --b.
