10.0_RC1 iwm panic

[Marc Baudoin <babafou%babafou.eu.org@localhost>]

Hi,

Since I upgraded my laptop to 10.0_RC1 a little over a month ago,
I've experienced three panics with the iwm driver.  Here's the
iwm0 I have in my laptop:

[     1,041044] iwm0 at pci3 dev 0 function 0: Intel Dual Band Wireless AC 8260 (rev. 0x3a)
[     1,041044] iwm0: interrupting at msi4 vec 0

Panics always happened while compiling mail/thunderbird on a
mechanical hard drive (I cannot compile it anymore on my small
SSD because newer versions require too much free space). Yes,
this has nothing in common with Wi-Fi but that's what I
experienced.

The panics happen after many of this kind of message in the
kernel log:

[ 20699,125473] iwm0: autoconfiguration error: unhandled firmware response 0x8544 0x44/0x2c4208 rx ring 87[0]
[ 20699,125473] iwm0: autoconfiguration error: unhandled firmware response 0xfcce 0xce/0xd1399214 rx ring 127[99]
[ 20699,125473] iwm0: autoconfiguration error: unhandled firmware response 0xe0 0xe0/0x400d rx ring 0[0]

Then:

[ 20701,655451] panic: m_copydata(0xffff8d4601653000,104,0,0xffffc3842fe4f000): m=NULL, off=0 (0), len=16 (88)
[ 20701,655451] cpu0: Begin traceback...
[ 20701,655451] vpanic() at netbsd:vpanic+0x183
[ 20701,655451] panic() at netbsd:panic+0x3c
[ 20701,665448] m_copydata.part.0() at netbsd:m_copydata.part.0+0xe9
[ 20701,665448] bus_dmamap_sync() at netbsd:bus_dmamap_sync+0x263
[ 20701,665448] iwm_start() at netbsd:iwm_start+0x6f2
[ 20701,665448] if_transmit() at netbsd:if_transmit+0x140
[ 20701,665448] ether_output() at netbsd:ether_output+0x36b
[ 20701,665448] ip_if_output() at netbsd:ip_if_output+0x86
[ 20701,665448] ip_output() at netbsd:ip_output+0xf04
[ 20701,665448] tcp_output() at netbsd:tcp_output+0x1622
[ 20701,665448] tcp_input() at netbsd:tcp_input+0xe80
[ 20701,665448] ipintr() at netbsd:ipintr+0x803
[ 20701,665448] softint_dispatch() at netbsd:softint_dispatch+0x95
[ 20701,665448] DDB lost frame for netbsd:Xsoftintr+0x4c, trying 0xffffc3842f99d0f0
[ 20701,665448] Xsoftintr() at netbsd:Xsoftintr+0x4c
[ 20701,665448] --- interrupt ---
[ 20701,665448] acda0ff91521d306:
[ 20701,665448] cpu0: End traceback...

The iwm driver has always been problematic (transfer rates are
way lower compared to the same system running Linux, for
instance) but it seems worse in 10.  Getting a DHCP lease also
often requires manually running dhcpcd after booting.

I'll be happy to test patches, if anybody have an idea on how to
solve these panics.