kern/77026: umount-ing non-existent device panics system

[Mikhail Teterin]

>Number:         77026
>Category:       kern
>Synopsis:       umount-ing non-existent device panics system
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Feb 02 18:10:21 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Mikhail Teterin
>Release:        FreeBSD 5.3-STABLE i386
>Organization:
Virtual Estates, Inc.
>Environment:

>Description:

	Every once in a while, a user forgets to umount the file system
	on a USB "flash-drive" before pulling the device out.

	The umass-device duly disappears upont the pull-out, but the
	mount-entry does not. Trying to umount such "fantom" devices
	results in "device not configured" errors.

	umount-ing with the `-f' switch crashes the system.

	I doubt, this is a USB-specific problem -- it is just the
	easiest way to reproduce the problem. CD-ROMs have hardware
	protection against this, but disconnecting a hard
	disk and rescanning the bus will, most probably, lead to the
	same situation.

	Note, that this happens even when no writes await and no
	files are open on the removed devices. `mount -oro -u',
	for example, succeds.

>How-To-Repeat:

	See description.

>Fix:

	Remember to umount. Still, panic is hardly a reasonable
	reaction.
>Release-Note:
>Audit-Trail:
>Unformatted: