K 10
svn:author
V 3
mjg
K 8
svn:date
V 27
2016-09-04T08:58:35.639792Z
K 7
svn:log
V 357
cache: manage negative entry list with a dedicated lock

Since negative entries are managed with a LRU list, a hit requires a
modificaton.

Currently the code tries to upgrade the global lock if needed and is
forced to retry the lookup if it fails.

Provide a dedicated lock for use when the cache is only shared-locked.

Reviewed by:	kib
MFC after:	1 week

END