Re: [follow-up] Fatal trap 12 in r195146+ in netisr_queue_internal

John Baldwin wrote:
> On Tuesday 21 July 2009 6:59:36 am Kamigishi Rei wrote:
>   
>> Everything goes fine until - under heavy load on an interface, usually - 
>> we reach a point where:
>> 1. m->mtx_lock is 4 (== MTX_UNOWNED).
>> 2. v is assigned mtx_lock's value (4 == MTX_UNOWNED).
>> 3. condition (v == MTX_UNOWNED) fails.
>>     
> This will not happen.  If you look at the disassembly you will see this can't 
> happen either.  Do you have a crashdump from a crash?
>   
I've got about 40 crash dumps on unmodded (without debug code) kernel, 
and 3 or 4 with debug stuff (KASSERTs added by me).
I can reproduce this on my test server (Core2 Duo 3.0, 4GB RAM), on my 
home PC (Core2 Quad 2.5), and in VMWare with 2 CPUs in VT-x mode on my 
laptop.
It can't be reproduced on single-CPU single-core (including 
hyperthreaded) systems.

Quoting,

(kgdb) fr 6
#6  0xffffffff80586255 in _mtx_lock_sleep (m=0xffffffff80e60823, 
tid=18446742977255365296, opts=Variable "opts" is not available.
) at /usr/src/sys/kern/kern_mutex.c:407
407                     owner = (struct thread *)(v & ~MTX_FLAGMASK);

(kgdb) print m->mtx_lock
$14 = 4
(kgdb) print v
$15 = 21946368

--
Kamigishi Rei
KREI-RIPE