kern/77289: system hangs while trying to unmount previously removed media

[Björn König]

>Number:         77289
>Category:       kern
>Synopsis:       system hangs while trying to unmount previously removed media
>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 09 02:40:22 GMT 2005
>Closed-Date:
>Last-Modified:
>Originator:     Björn König
>Release:        FreeBSD 5.3-RELEASE-p4 i386
>Organization:
>Environment:
System: FreeBSD hoppel.local 5.3-RELEASE-p4 FreeBSD 5.3-RELEASE-p4 #0: Mon Jan 10 10:02:44 CET 2005 root at hoppel.local:/usr/obj/usr/branch/RELENG_5_3/src/sys/HOPPEL i386


	
>Description:
	The system hangs while trying to unmount a filesystem of a removable media
	which was already physically removed and also if it was inserted again before.
	This concerns floppy disks. I also noticed similar odd behaviour with usb
	pen drives, but the system reboots instead and there is lot of console output.

>How-To-Repeat:
	mount a floppy disk

		% mount /dev/fd0 /mnt

	remove media now and unmount the file system
		
		% umount /mnt
	
	the following message appears on console:
		
		fsync: giving up on dirty: 0xc1ec5420: tag devfs, type VCHR,
		usecount 4, writecount 0, refcount 4, flags (VV_OBJBUF),
		lock type devfs: EXCL (count 1) by thread 0xc19adaf0 (pid 590)
		dev fd0

	and mount shows that the filesystem is still mounted. trying to unmount
	it twice let the system stop working immediately.

	a similar case occurs if you mount a floppy disk, remove media, insert
	disk again and then unmount the file system:
	
		umount: unmount of /mnt failed: Device not configured

	try to unmount it twice - system hangs.
>Fix:

>Release-Note:
>Audit-Trail:
>Unformatted: