Date: Fri, 08 Feb 2002 20:17:50 -0500 From: Bill Kish <kish@coyotepoint.com> To: hackers <freebsd-hackers@FreeBSD.ORG> Subject: Debugging double page fault Message-ID: <3C6478BE.BE6F5A70@coyotepoint.com>
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Hi All,
I've recently started seeing "double fault" panics on a formerly FreeBSD
2.2.8 based system (It's running 2.2.8 as a somewhat embedded OS, so please
don't flame me about being back rev!)
The stack trace looks like:
$ gdb -k kernel.0 vmcore.0
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under certain conditions; type "show copying" to see the conditions.
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GDB 4.16 (i386-unknown-freebsd),
Copyright 1996 Free Software Foundation, Inc...(no debugging symbols
found)...
IdlePTD 1aa000
current pcb at 1967a0
panic: double fault
#0 0xf010cf63 in boot ()
(kgdb) bt
#0 0xf010cf63 in boot ()
#1 0xf010d232 in panic ()
#2 0xf0176f5a in trap_fatal ()
#3 0xf0176a1c in trap_pfault ()
#4 0xf01766df in trap ()
#5 0xf012baae in vget ()
#6 0xf01558dc in ffs_sync ()
#7 0xf012cf7b in sync ()
#8 0xf010ce2d in boot ()
#9 0xf010d232 in panic ()
#10 0xf0176ff0 in trapwrite ()
(kgdb)
My rough understanding is that double faults are usually the result of
running out of stack, and that the underlying cause of the panic can probably
be uncovered if I can find the previous stack .
Can anyone point me towards some hints for debugging this sort of crash. Any
advice greatly appreciated.
-=BK
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