freebsd-5.4-stable panics

Fri Sep 30 08:25:37 PDT 2005

On 9/30/05, John Baldwin <jhb at freebsd.org> wrote:

> 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?

 I had a small program which could reproduce this panic in 10 seconds, it
was basically creating empty threads and calling kvm_getprocs() in the same
time. Anyway the patch was able to stop the program from panicing.
The panic is also reproducible in RELENG_6 and HEAD IIRC.

> On 9/29/05, Robert Watson <rwatson at 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
> > > _______________________________________________
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> --
> John Baldwin <jhb at FreeBSD.org> <>< http://www.FreeBSD.org/~jhb/<http://www.freebsd.org/~jhb/>
> "Power Users Use the Power to Serve" = http://www.FreeBSD.org<http://www.freebsd.org/>
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