"umount -f" Complete system crash...

Modulok modulok at gmail.com
Sun Jul 29 04:09:46 UTC 2007

Someone brought me a camera they were having trouble with: winXP
refused to mount the file system. I tried it on FreeBSD 6.1-RELEASE,
"mount_msdosfs /dev/da0s1 /mnt", no problems. I recovered all of their
photos. I attempted to "umount /mnt" and encountered an error,
something along the lines of cannot contact device, (I don't remember
exactly. No, I wasn't in the directory I was attempting to umount.).
No other process was communicating with the device, according to the
camera it was 'idle'. I issued a "umount -f /mnt" command. The entire
system locked up for a few seconds (maybe 4) and then CRASH! I found
myself looking at my BIOS output as the system reboots.

1. Obviously, why did FreeBSD crash? (More specifically what could
cause a crash in this situation?)
2. How do I find out, why it crashed?
3. Did I do something terribly unorthodox to invoke this crash, given
the situation? If so, what could be done different?

Any pointers would be appreciated.

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