On 15.12.2013 22:22, Eitan Adler wrote:
On Sun, Dec 15, 2013 at 3:23 AM, Eitan Adler <li...@eitanadler.com> wrote:
FreeBSD gravity.local 11.0-CURRENT FreeBSD 11.0-CURRENT #7 r259286:
Fri Dec 13 00:33:37 EST 2013
eitan@gravity.local:/usr/obj/usr/src/sys/EADLER  amd64

Complete textdump here: http://people.freebsd.org/~eadler/files/core.txt.1

My kernel is built with complete debug symbols, INVARIANTS, ddb, etc.
but no WITNESS.

I have vt and vt_vga enabled but not sc and vga (newcons, but not syscons).

Replying to myself with more data:

gdb$ list kern_timeout.c
Can't find member of namespace, class, struct, or union named "kern_timeout.c"
Hint: try 'kern_timeout.c<TAB> or 'kern_timeout.c<ESC-?>
(Note leading single quote.)
gdb$ list kern_timeout.c:700
695                     lastfunc = c_func;
696             }
697     #endif
698             CTR1(KTR_CALLOUT, "callout %p finished", c);
699             if ((c_flags & CALLOUT_RETURNUNLOCKED) == 0)
700                     class->lc_unlock(c_lock);
701     skip:
702             CC_LOCK(cc);
703             KASSERT(cc->cc_exec_entity[direct].cc_curr == c,
("mishandled cc_curr"));
704             cc->cc_exec_entity[direct].cc_curr = NULL;
gdb$ p c
$1 = (struct callout *) 0xffffffff812121f8
gdb$ p *c
$2 = {
   c_links = {
     le = {
       le_next = 0xfffffe0005f00318,
       le_prev = 0xffffffff813aa690
     sle = {
       sle_next = 0xfffffe0005f00318
     tqe = {
       tqe_next = 0xfffffe0005f00318,
       tqe_prev = 0xffffffff813aa690
   c_time = 0x2c0d9170f2f51,
   c_precision = 0xeffffeea,
   c_arg = 0xffffffff81212148,
   c_func = 0xffffffff8067e6e0 <vt_switch_timer>,
   c_lock = 0x0,
   c_flags = 0x80,
   c_cpu = 0x0

 From the 'vt_switch_timer' function it appears that something is wrong with vt.

In addition avg@ mentioned that he wonders why class->lc_lock(c_lock,
...) is protected by if (c_lock != NULL) but class->lc_unlock(c_lock)
does not have that guard.

It worked so far because callout_init() sets CALLOUT_RETURNUNLOCKED flag if there is no callout lock. I am not sure whether we should better add check or assertion to _callout_init_lock().

So either VT passes something odd/NULL pointer to callout_init_mtx(), or something overwrites the callout structure after scheduling the callout.

Alexander Motin
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