kern/38135: vfs_busy/vfs_trybusy confusion

[ad%netbsd.org@localhost]

>Number:         38135
>Category:       kern
>Synopsis:       vfs_busy/vfs_trybusy confusion
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Sun Mar 02 10:20:00 +0000 2008
>Originator:     Andrew Doran
>Release:        5.99.55
>Organization:
The NetBSD Project
>Environment:
n/a
>Description:
In some places we do vfs_trybusy(), e.g. when getting mount status.
Other threads can have the mount write locked, causing innocuous 
operations to fail when they shouldn't.

>How-To-Repeat:
Code inspection.
>Fix:
Review all uses of vfs_busy+vfs_trybusy and/or consider not failing
vfs_trybusy unless the mount is gone or unmount is in progress.