From owner-freebsd-stable  Mon Feb 22 15:42:29 1999
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Subject: Re: 3.1-RELEASE crash dump with -g kernel, 'page fault in kernel mode' 
In-Reply-To: Message from Rahul Dhesi <dhesi@rahul.net> 
   of Fri, 19 Feb 99 19:33:01 -0800
Date: Mon, 22 Feb 99 15:41:50 -0800
From: Rahul Dhesi <dhesi@rahul.net>
Sender: owner-freebsd-stable@FreeBSD.ORG
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X-Loop: FreeBSD.ORG

I have been looking through the open PRs, and found this one that's
interesting:

   kern/2717
   Fatal trap 12: page fault while in kernel mode

It contains this annotation made on Date: Wed, 12 Feb 1997 17:40:11 +1100:

   The standard (syscons) console driver and perhaps the pcvt console
   driver have some races when kernel printfs from interrupt handlers
   are mixed with normal console output.

   Workarounds: don't put (m)any printfs in interrupt handlers, or don't
   use /dev/ttyv0 for normal applications (it's still used for console
   output by syslogd etc so this only reduces the problem), or use a
   serial console.

I wonder if this is still a problem in current versions of FreeBSD?  If
so, this might explain a number of different reports of 'page fault
while in kernel mode' that I have seen, including mine (below).  Would
somebody who is familar with the internals of the syscons console driver
please comment?

What's interesting is that I have a machine (no keyboard) running
3.0-RELEASE doing News processing that never panics like this.  It
has a /boot.config file that contains '-h', which is supposed to force
use of the serial port as console.

But a number of machine running any of 3.0-RELEASE, 3.1-RELEASE, and
various 3.0 snapshots, all with keyboard and display connected, and not
having a /boot.config file, have panic'd with 'page fault while in
kernel mode'.  *IF* the use of the display is the problem, then I will
be very happy, because it's easily fixable by switching to the serial
console.  I am going to try this.

If anybody else has encountered these panics, please comment.

Rahul


> Date:  Fri, 19 Feb 99 19:33:01 PST
> From:  Rahul Dhesi <dhesi@rahul.net>
> To:    stable@freebsd.org
> Message-Id: <199902200333.AA27605@waltz.rahul.net>
> Subject: 3.1-RELEASE crash dump with -g kernel, 'page fault in kernel
     *** mode'

> I am now running 3.1-RELEASE with a kernel that was compiled with -g,
> and I have a crash dump available.  If anybody is interested in getting
> more details, I will be happy to provide them to you -- please contact
> me.  Below is a little of what I have.  This particular problem (page
> fault in kernel mode) has been occurring with various STABLE snapshots.
> 
> Rahul
> 
> 
> Fatal trap 12: page fault while in kernel mode
> fault virtual address   = 0x48
> fault code              = supervisor write, page not present
> 
> ...
> 
> (kgdb) where
> #0  0xf015d86b in boot ()
> #1  0xf015daf0 in at_shutdown ()
> #2  0xf024c305 in trap_fatal ()
> #3  0xf024bfe3 in trap_pfault ()
> #4  0xf024bc5a in trap ()
> #5  0xf02117c8 in acquire_lock ()
> #6  0xf021440e in softdep_disk_io_initiation ()
> #7  0xf018caba in spec_strategy ()
> #8  0xf018c24d in spec_vnoperate ()
> #9  0xf021fe75 in ufs_vnoperatespec ()
> #10 0xf021f87b in ufs_strategy ()
> #11 0xf021fe45 in ufs_vnoperate ()
> #12 0xf017a023 in bwrite ()
> #13 0xf017e55a in vop_stdbwrite ()
> #14 0xf017e3a5 in vop_defaultop ()
> #15 0xf021fe45 in ufs_vnoperate ()
> #16 0xf017a9b7 in vfs_bio_awrite ()
> #17 0xf021966b in ffs_fsync ()
> #18 0xf0217b7b in ffs_sync ()
> #19 0xf0182e6f in sync ()
> #20 0xf015d6b1 in boot ()
> #21 0xf015daf0 in at_shutdown ()
> #22 0xf024c305 in trap_fatal ()
> ---Type <return> to continue, or q <return> to quit---
> #23 0xf024bfe3 in trap_pfault ()
> #24 0xf024bc5a in trap ()
> #25 0xf01eb2ad in tulip_rx_intr ()
> #26 0xf01eb9f3 in tulip_intr_handler ()
> #27 0xf01ebb51 in tulip_intr_normal ()
> 
> == END ==
> 
> 
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