From owner-freebsd-i386@FreeBSD.ORG  Wed Sep  5 05:49:15 2007
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Date: Wed, 5 Sep 2007 15:47:49 +1000 (EST)
From: Bruce Evans <brde@optusnet.com.au>
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To: Dmitry Andrianov <666.root@gmail.com>
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Cc: freebsd-gnats-submit@FreeBSD.org, freebsd-i386@FreeBSD.org
Subject: Re: i386/116100: Fatal trap 12 right after reboot (da0s1error = 6)
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On Wed, 5 Sep 2007, Dmitry Andrianov wrote:

>> Environment:
> 7.0-CURRENT-200704 FreeBSD 7.0-CURRENT-200704 #0: Sun Apr  1 14:46:54 UTC 2007  root@almeida.cse.buffalo.edu:/usr/obj/usr/src/sys/GENERIC  i386

This is old, so not broken by me :-).

>> Description:
> bash-2.05b#mount -t msdosfs /dev/da0s1 /mnt
> bash-2.05b#
> ..
> bash-2.05b#reboot
>
> <118>Sep  3 18:54:08 zingel reboot: rebooted by root
> <118>Sep  3 18:54:08 zingel syslogd: exiting on signal 15
> Waiting (max 60 seconds) for system process `vnlru' to stop...done
> Waiting (max 60 seconds) for system process `bufdaemon' to stop...done
> Waiting (max 60 seconds) for system process `syncer' to stop...
> Syncing disks, vnodes remaining...1 0 0 0 done
> All buffers synced.
> g_vfs_done():da0s1[READ(offset=65536, length=4096)]error = 6

An i/o error in unmount is likely to cause problems.  The system never
gives up trying to write unwriteable buffers, and tends to panic trying
to write them later.  I recently fixed some panics in unmount (not yet
committed), but the fix is to make unmount not fail, and that won't
help for reboot because unmount cannot fail.  msdosfs and perhaps even
ffs normally does a write in unmount _after_ the "All buffers synced"
message has been printed.

> (da0:dead_sim0:0:0:0): Synchronize cache failed, status == 0x8, scsi status == 0x0
> (da0:dead_sim0:0:0:0): removing device entry

Removing a device entry is a wrong thing to do if there is i/o pending on
the device.  It would work if the i/o is reattached to dead_something,
but that apparently isn't done.

You need to figure out what caused the i/o error -- is it msdosfs, the
disk driver or the disk?

Bruce