Date: Thu, 16 Jan 1997 16:50:02 -0800 (PST) From: j@uriah.heep.sax.de (J Wunsch) To: freebsd-bugs Subject: Re: kern/2494: page faults Message-ID: <199701170050.QAA27704@freefall.freebsd.org>
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The following reply was made to PR kern/2494; it has been noted by GNATS.
From: j@uriah.heep.sax.de (J Wunsch)
To: spatula@gulf.net (Prisoner)
Cc: freebsd-gnats-submit@freefall.freebsd.org
Subject: Re: kern/2494: page faults
Date: Thu, 16 Jan 1997 20:23:43 +0100
As Prisoner wrote:
> fault virtual address = 0x7200c4c
> fault code = supervisor read, page not present
> instruction pointer = 0x8:0xf017c4b4
> code segment = base 0x0, limit 0xfffff, type 0x1b
> = DPL 0, pres 1, def32 1, gran 1
> processor eflags = trace/trap, interrupt enabled, resume, IOPL=0
> current process = 4 (update)
> interrupt mask =
> kernel: type 12 trap, code=0
> breakpoint at _ffs_update +0xa4: cmpl $0x1,0x52c(%ebx)
>
> It's always within a few instructions to this location.
This is in /sys/ufs/ffs/ffs_inode.c:
int
ffs_update(ap)
struct vop_update_args /* {
struct vnode *a_vp;
struct timeval *a_access;
struct timeval *a_modify;
int a_waitfor;
} */ *ap;
{
...
fs = ip->i_fs;
/*
* Ensure that uid and gid are correct. This is a temporary
* fix until fsck has been changed to do the update.
*/
if (fs->fs_inodefmt < FS_44INODEFMT) { /* XXX */
^^^^
here
If it were a genuine bug in the code, it should always happen at the
same spot, not just `somewhere around'.
The fault VA looks suspicous, it's 0x7200c4c - 0x52c = 0x72000720.
Somehow, the ip->i_fs pointer has been trashed by dumping the short
value 0x720 over it. Incidentally, this value is just a space in the
video screen buffer, together with the default attribute 0x7 (light
gray on black). It looks like part of your screen updates go wild
into the memory.
--
cheers, J"org
joerg_wunsch@uriah.heep.sax.de -- http://www.sax.de/~joerg/ -- NIC: JW11-RIPE
Never trust an operating system you don't have sources for. ;-)
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