kern/38039: genfs+ufs inode locking problem

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>Number:         38039
>Category:       kern
>Synopsis:       genfs+ufs inode locking problem
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Feb 15 23:15:00 +0000 2008
>Originator:     Andrew Doran
>Release:        4.99.54
>Organization:
The NetBSD Project
>Environment:
n/a
>Description:
ufs_gop_markupdate modifies inode::i_flag without holding the vnode lock.
Under the right circumstances inode updates could be delayed or never
flushed to disk. 

>How-To-Repeat:
Code inspection.
>Fix:
Using atomics to maintain i_flag seems too expensive. We could introduce
another field to be maintained using atomic ops, and combine it with
i_flag in ffs_itimes(). If we had inode locks it would probably make
sense to use those.