Fatal trap 12: page fault while in kernel mode

[John Baldwin]

On Wednesday 07 December 2005 02:47 am, Yuri Khotyaintsev wrote:
> On Friday 02 December 2005 14.54, John Baldwin wrote:
> > On Friday 02 December 2005 05:00 am, Yuri Khotyaintsev wrote:
> > > I have the following panic occurring several times a week. The machine
> > > is an NFS server, and it usually panics early in the morning, when
> > > first people try to access it. After reboot it may work OK for 1-2
> > > days, and then panics again. I have tried changing memory and replacing
> > > disk which was exported via NFS, but nothing helped :(
> > >
> > > Any suggestion on how to fix this panic will be very much appreciated !
> >
> > This panic (in propagate_priority) is usually caused when a thread goes
> > to sleep while holding a mutex (which is forbidden).  If you enable
> > INVARIANTS and/or WITNESS you should get a better panic, and with WITNESS
> > you will even be warned when a thread goes to sleep while holding a
> > mutex.  However, these options do introduce considerable execution
> > overhead, and sometimes that overhead changes the timing enough to hide
> > the race. :(
>
> Here are the two panics which I got with INVARIANTS and WITNESS enabled.
>
> Unread portion of the kernel message buffer:
> Memory modified after free 0xc4759e00(508) val=0 @ 0xc4759e00
> panic: Most recently used by UFS dirhash

Well, this isn't the panic I was expecting, but it points to something 
trashing free'd memory via a stale pointer or some such.  You might be able 
to use MEMGUARD to track this down.

-- 
John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve"  =  http://www.FreeBSD.org