Date: Fri, 30 Sep 2005 08:54:47 -0400 From: John Baldwin <jhb@FreeBSD.org> To: freebsd-hackers@freebsd.org, Antoine Pelisse <apelisse@gmail.com> Subject: Re: freebsd-5.4-stable panics Message-ID: <200509300854.48210.jhb@FreeBSD.org> In-Reply-To: <61c746830509300224g3d79cbe4ve55e8b0b27004fc3@mail.gmail.com> References: <da4a53d805092310237d732554@mail.gmail.com> <61c746830509300215x7833746ew60896c4c1338ec65@mail.gmail.com> <61c746830509300224g3d79cbe4ve55e8b0b27004fc3@mail.gmail.com>
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On Friday 30 September 2005 05:24 am, Antoine Pelisse wrote: > Hi Robert, > I don't think your patch is correct, the total linked list can be broken > while the lock is released, thus just passing the link may not be enough > I have submitted a PR[1] for this a month ago but nobody took care of it > yet Regards, > Antoine Pelisse > > [1] http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/84684 I think this patch looks ok. Robert, can you get the original panic on this thread tested against this patch? > On 9/29/05, Robert Watson <rwatson@freebsd.org> wrote: > > On Thu, 29 Sep 2005, Rob Watt wrote: > > > On Thu, 29 Sep 2005, Robert Watson wrote: > > >> Could you dump the contents of *td and *td->td_proc for me? I'm quite > > >> interested to know what the value in td->td_proc->p_state is, among > > > > other > > > > >> things. If I could also have you generate a dump of the KSE group > > >> structures in td->td_proc->p_ksegrps and the threads in > > >> td->td_proc->p_threads. > > > > > > I've attached a file with many of the values you have asked for. We > > > looked at some of the threads referenced by td->td_proc->p_threads, but > > > we weren't sure we were walking the list correctly. Do you have any > > > tips > > > > > > for walking those thread lists? > > > > > >> Could you tell me if the program named by p->p_comm is linked against > > >> a threading library? If it's a custom app, you may already know, and > > >> if not, you can run ldd on the application to see what it is linked > > >> against. > > > > > > The programs named by p->p_comm is linked against the pthreads library. > > > > This seems to be enough information to at least track this down a bit: > > td_ksegrp is NULL, rather than a corrupt value, which suggests that the > > thread is incompletely initialized. Other hints that this are the case > > are that td_critnest is 1 (as is set when it is allocated), and the state > > is TDS_INACTIVE. Some other fields are set though, such as td_oncpu, > > which is normally initialized to NOCPU. > > > > > (kgdb) p *td > > > $1 = {td_proc = 0xffffff004aa9f000, td_ksegrp = 0x0, td_plist = > > > {tqe_next = 0xff ffff00b4798000, > > > tqe_prev = 0xffffff00a97ae010}, td_kglist = {tqe_next = > > > 0xffffff00b4798000, > > > tqe_prev = 0xffffff00a97ae020}, td_slpq = {tqe_next = 0x0, tqe_prev > > > = 0xffff ff001fac7c10}, td_lockq = { > > > tqe_next = 0xffffff00a97ae000, tqe_prev = 0xffffffffb6797a70}, > > > td_runq = {tq e_next = 0x0, > > > tqe_prev = 0xffffffff80608180}, td_selq = {tqh_first = 0x0, tqh_last > > > = 0xfff fff00633112c0}, > > > td_sleepqueue = 0xffffff00382b0400, td_turnstile = 0xffffff00c1712900, > > > td_umtx q = 0xffffff00d1207080, > > > td_tid = 100253, td_flags = 16777216, td_inhibitors = 0, td_pflags = > > > 128, td_d upfd = 0, td_wchan = 0x0, > > > td_wmesg = 0x0, td_lastcpu = 2 '\002', td_oncpu = 2 '\002', > > > td_owepreempt = 0 '\0', td_locks = 0, > > > td_blocked = 0x0, td_ithd = 0x0, td_lockname = 0x0, td_contested = > > > {lh_first = > > > 0x0}, td_sleeplocks = 0x0, > > > td_intr_nesting_level = 0, td_pinned = 0, td_mailbox = 0x0, td_ucred = > > > 0xfffff f00ad18f200, > > > td_standin = 0x0, td_upcall = 0x0, td_sticks = 0, td_uuticks = 0, > > > td_usticks = > > > 0, td_intrval = 0, > > > td_oldsigmask = {__bits = {0, 0, 0, 0}}, td_sigmask = {__bits = > > > {4294967295, 4 294967295, 4294967295, > > > 4294967295}}, td_siglist = {__bits = {0, 0, 0, 0}}, td_generation > > > = 14, td _sigstk = {ss_sp = 0x0, > > > ss_size = 0, ss_flags = 0}, td_kflags = 0, td_xsig = 0, > > > td_profil_addr = 0, td_profil_ticks = 0, > > > td_base_pri = 182 '\uffff', td_priority = 182 '\uffff', td_pcb = > > > 0xffffffffb68 dcd10, td_state = TDS_INACTIVE, > > > td_retval = {1, 29309280}, td_slpcallout = {c_links = {sle = {sle_next > > > = 0x0}, > > > tqe = {tqe_next = 0x0, > > > tqe_prev = 0xffffff001fac7d80}}, c_time = 55907602, c_arg = > > > 0xffffff0063 311260, > > > c_func = 0xffffffff802e32a0 <sleepq_timeout>, c_mtx = 0x0, c_flags = > > > 16}, td _frame = 0xffffffffb68dcc40, > > > td_kstack_obj = 0xffffff0087f93d20, td_kstack = 18446744072477315072, > > > td_kstac k_pages = 4, > > > td_altkstack_obj = 0x0, td_altkstack = 0, td_altkstack_pages = 0, > > > td_critnest = 1, td_md = { > > > md_spinlock_count = 1, md_saved_flags = 582}, td_sched = > > > 0xffffff0063311488} > > > > I'm not familiar with the internals of the thread and KSE life cycle > > here, > > > > so I think we'll need to look to those more familiar with this to > > understand what of two things may be going on: > > > > (1) Is the fact that td_ksegrp != NULL an invariant for a connected > > thread, and that kern_proc is relying on that but the thread code is > > failing to implement it safely? > > > > (2) Is td_ksegrp sometimes left legitimately as NULL as part of the > > thread life cycle, and that kern_proc incorrectly assumes that it is > > never NULL when hooked up to a thread. > > > > This suggests a possible work-around of simply testing td_ksegrp for NULL > > in kern_proc in order to avoid this, while attempting to resolve whether > > an invariant is violated (or incorrectly assumed), which might require > > some serious thinking and a solution that is non-trivial. Something like > > the following might work in the mean time: > > > > Index: kern_proc.c > > =================================================================== > > RCS file: /home/ncvs/src/sys/kern/kern_proc.c,v > > retrieving revision 1.231 > > diff -u -r1.231 kern_proc.c > > --- kern_proc.c 27 Sep 2005 18:03:15 -0000 1.231 > > +++ kern_proc.c 29 Sep 2005 20:50:33 -0000 > > @@ -882,6 +882,8 @@ > > } else { > > _PHOLD(p); > > FOREACH_THREAD_IN_PROC(p, td) { > > + if (td->td_ksegrp == NULL) > > + continue; > > fill_kinfo_thread(td, &kinfo_proc); > > PROC_UNLOCK(p); > > error = SYSCTL_OUT(req, (caddr_t)&kinfo_proc, > > > > I'm going to forward off your e-mail to the threads@ list and see if > > anyone there wants to talk some more about this. If you don't mind > > testing the above patch to see if this is a workable work-around, we may > > want to think about getting it committed in the mean time. > > > > Thanks, > > > > Robert N M Watson > > _______________________________________________ > > freebsd-hackers@freebsd.org mailing list > > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > > To unsubscribe, send any mail to > > "freebsd-hackers-unsubscribe@freebsd.org" > > _______________________________________________ > freebsd-hackers@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-hackers > To unsubscribe, send any mail to "freebsd-hackers-unsubscribe@freebsd.org" -- John Baldwin <jhb@FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/ "Power Users Use the Power to Serve" = http://www.FreeBSD.org
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