panic: Assertion in_epoch(net_epoch_preempt) failed at ... src/sys/net/if.c:3694

This was on my laptop (build machine, which was updated in parallel,
but uses a different NIC, had no issues) after a src update from
r353176 to r353298; laptop's NIC is wlan(4) (which is iwn(4), in
this case).

The ddb "dump" command recorded a dump, which I managed to capture; the
information may be found at
http://www.catwhisker.org/~david/FreeBSD/head/r353298/

Here's the backtrace (from
http://www.catwhisker.org/~david/FreeBSD/head/r353298/core.txt.0):

panic: Assertion in_epoch(net_epoch_preempt) failed at /usr/src/sys/net/if.c:3694
cpuid = 3
time = 1570535588
KDB: stack backtrace:
db_trace_self_wrapper() at 0xffffffff8049ebab = db_trace_self_wrapper+0x2b/frame 0xfffffe103196a8b0
vpanic() at 0xffffffff80b979bd = vpanic+0x19d/frame 0xfffffe103196a900
panic() at 0xffffffff80b97753 = panic+0x43/frame 0xfffffe103196a960
if_delmulti_ifma_flags() at 0xffffffff80ca9231 = if_delmulti_ifma_flags+0x141/frame 0xfffffe103196a990
inm_release_task() at 0xffffffff80d3211c = inm_release_task+0x1ac/frame 0xfffffe103196a9f0
gtaskqueue_run_locked() at 0xffffffff80be1c59 = gtaskqueue_run_locked+0xf9/frame 0xfffffe103196aa40
gtaskqueue_thread_loop() at 0xffffffff80be1a18 = gtaskqueue_thread_loop+0x88/frame 0xfffffe103196aa70
fork_exit() at 0xffffffff80b55714 = fork_exit+0x84/frame 0xfffffe103196aab0
fork_trampoline() at 0xffffffff8101f28e = fork_trampoline+0xe/frame 0xfffffe103196aab0
--- trap 0, rip = 0, rsp = 0, rbp = 0 ---
KDB: enter: panic


I was unable to boot from (yesterday's) kernel.old -- loader whined
something about a header mismatch (I think -- there was a fair bit
of text-overwriting).  I was able to extract the dump by rebooting
from the same kernel, but disabling the NIC first, then switching
to a vty, logging in, and I managed to run "sync" a few times before
it panicked again.

I expect that for tomorrow, I'll end up "cloning" the stable/12
slice over the top of the head slice, then upgrade from stable/12
to head again.

Peace,
david
-- 
David H. Wolfskill				david_at_catwhisker.org
I am amazed that anyone would condone what Trunp has publicly admitted he did.

See http://www.catwhisker.org/~david/publickey.gpg for my public key.