Bug 30594

panic: static sysctl oid too high: 684

(kgdb) bt
[...]
#10 0xc0189716 in sysctl_register_oid (oidp=0xc19710c0)
    at ../../../kern/kern_sysctl.c:127
#11 0xc01897f8 in sysctl_ctx_free (clist=0xc0cd3c68)
    at ../../../kern/kern_sysctl.c:192
(kgdb) list
191             while (e1 != NULL) {
192                     sysctl_register_oid(e1->entry);
193                     e1 = TAILQ_PREV(e1, sysctl_ctx_list, link);
194             }
(kgdb) print *e1->entry
$1 = {oid_parent = 0xc033d040, oid_link = {sle_next = 0x0}, oid_number = 684,
  oid_kind = -2113929215, oid_arg1 = 0xc0cd8540, oid_arg2 = 0,
  oid_name = 0xc0cd8550 "pcm0", oid_handler = 0, oid_fmt = 0xc0338b3d "N",
  oid_refcnt = 1}
(kgdb) printf "%x\n",e1->entry->oid_kind
82000001
 ^
 CTLFLAG_DYN

From src/sys/kern/kern_sysctl.c in sysctl_ctx_free() :
        /*
         * First perform a "dry run" to check if it's ok to remove oids.
         * XXX FIXME
         * XXX This algorithm is a hack. But I don't know any
         * XXX better solution for now...
         */

It appears in the comments of sysctl_ctx_free() that this function is a
hack.  It seems it sometimes has to re-register an oid, and sometimes
tries to re-register dynamic sysctls.  In that case it doesn't change
the oid_number of the oid, and just call sysctl_register_oid() which
panics because it is too high.

I'm not able to properly fix this function right now, because I don't
understand the reasons of this hack, however I can provide a patch
that sets the oid_number to OID_AUTO if it was greater or equal to
CTL_AUTO_START.  With this patch applied, I can now happily load and
unload my sound modules several times.

Fix: Note: It would perhaps be better to test oid_kind against CTLFLAG_DYN
instead of looking at the oid_number.
How-To-Repeat: 	# kldunload snd_es137x