Date: Mon, 30 Nov 2009 10:36:25 -0500 From: "Robert N. M. Watson" <rwatson@freebsd.org> To: =?iso-8859-1?Q?Eirik_=D8verby?= <ltning@anduin.net> Cc: pyunyh@gmail.com, weldon@excelsusphoto.com, freebsd-current@freebsd.org, Gavin Atkinson <gavin@freebsd.org> Subject: Re: FreeBSD 8.0 - network stack crashes? Message-ID: <EE2AA268-2309-4924-A3AD-1EC256E7BB2A@freebsd.org> In-Reply-To: <1DFC4992-E136-4674-BC0E-A6B1DAE12AF4@anduin.net> References: <A1648B95-F36D-459D-BBC4-FFCA63FC1E4C@anduin.net> <20091129013026.GA1355@michelle.cdnetworks.com> <74BFE523-4BB3-4748-98BA-71FBD9829CD5@anduin.net> <alpine.BSF.2.00.0911291427240.80654@fledge.watson.org> <34AD565D-814A-446A-B9CA-AC16DD762E1B@anduin.net> <A0C9ED20-5536-44E2-B26B-0F1AEC2AF79C@anduin.net> <BA47FDA1-1097-4C43-AF71-51E7227795B5@FreeBSD.org> <1DFC4992-E136-4674-BC0E-A6B1DAE12AF4@anduin.net>
next in thread | previous in thread | raw e-mail | index | archive | help
On 30 Nov 2009, at 08:40, Eirik =D8verby wrote: >>> Short follow-up: Making OpenBSD use TCP mounts (it defaults to UDP) = seems to solve the issue. >>>=20 >>> So this is a UDP-NFS-related problem, it would seem? >>=20 >> Could well be. Let's try another debugging tactic -- there are two = possible things going on here: resource leak, and resource exhaustion = leading to deadlock. If you shut down to single user mode from = multi-user, and let the system quiesce for a few minutes, then run = netstat -m, what does it look like? Do vast numbers of mbufs+clusters = get freed, or do they remain accounted for as allocated? >=20 > It's been sitting in single-user mode for about 15 minutes now, no = change in allocation. > I'll reboot in about 15 minutes, then try to mount from a FreeBSD box = using UDP - if that causes the same issues, I guess it's not an OpenBSD = specific issue but a UDP issue "in general". Next step would be to try = to reproduce the same between two VMs on my own box, as this box needs = to return to production soonish - if we manage to reproduce elsewhere.. This sounds like a good plan -- especially reproducing it on a = non-production box :-). I agree it's most likely that the OpenBSD NFS = client simply does something a little differently than the other NFS = clients you are dealing with, triggering an edge case in our NFS server = code. But, to be clear, I think it's much more likely that the bug is in = the NFS over UDP code than UDP itself, given the complexity of the NFS = code (although a UDP bug can't be ruled out). Robert >=20 > Other ideas/suggestions? >=20 > /Eirik >=20 >> (If they remain allocated, they were likely leaked, since most/all = sockets will have been closed, releasing their resources on shutdown to = single user when all processes are killed) >>=20 >> The theory of an mbuf leak in NFS isn't an unlikely theory -- the = socket code there continues to change, and rare edge cases frequently = lead to leaks (per my earlier e-mail). Perhaps there's a case the = OpenBSD client is triggering that other NFS clients normally don't. If = we think that's the case, the next step is usually to narrow down what = causes the leak to trigger a lot (i.e., the backup starting), and then = grab a packet trace that we can analyze with wireshark. We'll want to = look at the types of errors being returned for RPCs and, in particular, = if there's one that happens about the same number of times as the = resource has leaked over the same window, look at the code and see if = that error case is handled properly. >>=20 >> If this is definitely an NFS leak bug, we should get the NFS folks = attention by sticking "NFS mbuf leak" in the subject line and CC'ing = rmacklem/dfr. :-) >>=20 >> Robert >>=20 >>=20 >>=20 >>=20 >>> /Eirik >>>=20 >>> On 30. nov. 2009, at 11.22, Eirik =D8verby wrote: >>>=20 >>>> Hi, >>>>=20 >>>> I have something that might be more interesting than any counter = ... >>>> It seems to me as if the problem *only* manifests itself when an = OpenBSD box is backing up to this FreeBSD 8.0-NFS-ZFS server. All other = boxes are FreeBSD, and I have so far today been unable to reproduce the = problem from any of those. As soon as I interrupted the backup running = from OpenBSD, the mbuf cluster usage stabilized. >>>>=20 >>>> How's that for a mystery in the morning? >>>>=20 >>>> /Eirik >>>>=20 >>>> On 29. nov. 2009, at 15.29, Robert Watson wrote: >>>>=20 >>>>> On Sun, 29 Nov 2009, Eirik =D8verby wrote: >>>>>=20 >>>>>> I just did that (-rxcsum -txcsum -tso), but the numbers still = keep rising. I'll wait and see if it goes down again, then reboot with = those values to see how it behaves. But right away it doesn't look too = good .. >>>>>=20 >>>>> It would be interesting to know if any of the counters in the = output of netstat -s grow linearly with the allocation count in netstat = -m. Often times leaks are associated with edge cases in the stack = (typically because if they are in common cases the bug is detected = really quickly!) -- usually error handling, where in some error case the = unwinding fails to free an mbuf that it should free. These are = notoriously hard to track down, unfortunately, but the stats output = (especially where delta alloc is linear to delta stat) may inform the = situation some more. >>>>>=20 >>>>> Robert N M Watson >>>>> Computer Laboratory >>>>> University of Cambridge >>>>=20 >>>> _______________________________________________ >>>> freebsd-current@freebsd.org mailing list >>>> http://lists.freebsd.org/mailman/listinfo/freebsd-current >>>> To unsubscribe, send any mail to = "freebsd-current-unsubscribe@freebsd.org" >>>>=20 >>>=20 >>=20 >> _______________________________________________ >> freebsd-current@freebsd.org mailing list >> http://lists.freebsd.org/mailman/listinfo/freebsd-current >> To unsubscribe, send any mail to = "freebsd-current-unsubscribe@freebsd.org" >>=20 >=20
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?EE2AA268-2309-4924-A3AD-1EC256E7BB2A>