Re: panic: assertion failed in iflib_txq_drain()

From: Michael Tuexen <tuexen_at_FreeBSD.org>
Date: Sat, 18 Apr 2026 19:12:58 UTC
> On 18. Apr 2026, at 21:09, Drew Gallatin <gallatin@freebsd.org> wrote:
> 
> Sorry, looking into this now.  I did not test this change with the mp_ring path.. i don't see how fixing the counters could cause this panic.   Looking at it now..
Hi Drew,

I think https://reviews.freebsd.org/D56509 fixes it.

Best regards
Michael
> 
> Drew
> 
> On Sat, Apr 18, 2026, at 1:38 PM, Michael Tuexen wrote:
>> 
>> 
>> > On 18. Apr 2026, at 19:14, David Wolfskill <david@catwhisker.org> wrote:
>> > 
>> > On Sat, Apr 18, 2026 at 03:53:33PM +0200, Michael Tuexen wrote:
>> >> ...
>> >>> So... one of the machines on which I track head got this, as well -- my
>> >>> (mostly-)headless build machine.  (2 laptops, updated in sync with the
>> >>> build machine, did not panic.  One of those also uses a wired NIC.)
>> >> Do the network drivers of the machines not being affected use iflib?
>> > 
>> > Apparently not -- they are em(4), iwm(4), & iwn(4), while the panicking
>> > machine uses igb(4).
>> > 
>> >> I do see the problem also on one of my machines and local testing shows that
>> >> https://cgit.FreeBSD.org/src/commit/?id=3fade68cfdf95ee0b517b5d69b270bd8da633404 <https://cgit.freebsd.org/src/commit/?id=3fade68cfdf95ee0b517b5d69b270bd8da633404>
>> >> is the problem. At least reverting it locally resolves the problem.
>> >> Can you confirm this?
>> > 
>> > I can, and do:  after reverting main-n285140-3fade68cfdf9 & rebuilding,
>> > I am able to ssh in without issue; the machine reports:
>> > 
>> > freebeast(16.0-C)[2] uname -aUK
>> > FreeBSD freebeast.catwhisker.org 16.0-CURRENT FreeBSD 16.0-CURRENT #549 main-n285180-23a84efeb191: Sat Apr 18 17:01:25 UTC 2026     root@freebeast.catwhisker.org:/common/S3/obj/usr/src/amd64.amd64/sys/GENERIC amd64 1600015 1600015
>> > 
>> > Thanks!
>> You could also disable TSO. I will put up a review for a fix soon.
>> 
>> Best regards
>> Michael
>> > 
>> > Peace,
>> > david
>> > -- 
>> > David H. Wolfskill                              david@catwhisker.org
>> > 
>> > See https://www.catwhisker.org/~david/publickey.gpg for my public key.
>> 
>> 
>> 
>