Re: panic: assertion failed in iflib_txq_drain()

That is indeed the proper fix.   I just reviewed & tested it.  Thank you so much!

Until it lands, another workaround is to use the new, cheaper, faster, simpler iflib transmit routine by setting the tunable

dev.$NIC.$UNIT.iflib.simple_tx=1

Eg, dev.bnxt.0.iflib.simple_tx=1

In loader.conf

I plan to deprecate the current complex transmit routine (mp_ring) in favor of the simple mechanism, and I confess that I sometimes don't test "straightforward" changes like this on mp_ring.  I'll try to get better about that.

Drew

On Sat, Apr 18, 2026, at 3:12 PM, Michael Tuexen wrote:
> > On 18. Apr 2026, at 21:09, Drew Gallatin <[email protected]> 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 <[email protected]> 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     [email protected]:/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                              [email protected]
> >> > 
> >> > See https://www.catwhisker.org/~david/publickey.gpg for my public key.
> >> 
> >> 
> >> 
> > 
> 
>