kern/139718: all mounted fs don't get synced during reboot/shutdown with >= 1 mounted inaccessible device

[Alexander Best]

>Number:         139718
>Category:       kern
>Synopsis:       all mounted fs don't get synced during reboot/shutdown with >= 1 mounted inaccessible device
>Confidential:   no
>Severity:       serious
>Priority:       high
>Responsible:    freebsd-bugs
>State:          open
>Quarter:        
>Keywords:       
>Date-Required:
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Sun Oct 18 12:40:01 UTC 2009
>Closed-Date:
>Last-Modified:
>Originator:     Alexander Best
>Release:        9.0-CURRENT
>Organization:
>Environment:
FreeBSD otaku 9.0-CURRENT FreeBSD 9.0-CURRENT #0 r197914: Sat Oct 10 02:58:19 CEST 2009     root at otaku:/usr/obj/usr/src/sys/ARUNDEL  i386
>Description:
when the system is being shutdown or rebooted and a mounted device isn't accessible any longer all other mounted devices aren't being synced correctly and thus marked dirty. this also happens if the inaccessible device was mounted read-only.

the reboot/shutdown sequence hangs after the message "All buffers synced.". after a reset all previosly mounted sttorage devices need to be fsck'ed.

see this thread for further info: http://lists.freebsd.org/pipermail/freebsd-current/2009-October/012679.html

Matthias Andree described the problem like this:

"1. If the device for one file system is gone, why would I mark *other* file
systems dirty? There is no reason to do so.

2. If a file system was mounted read-only, and its device is removed, there are
by definition ZERO dirty buffers that we need to synch on shutdown, so why does
the premature unplug-readonly-before-unmount spoil the shutdown?"
>How-To-Repeat:
1. mount a removable device (e.g. an usb stick) (better use -r to prevent data
loss)
2. unplug the device (without unmounting it)
3. `shutdown -r now`
>Fix:


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