To purge an nfsd-authentication cache, we set the flush time to later than
last-refresh time in the cache and call cache_flush.  The easiest way to
find 'later than last-refresh' is 'now+1'.

This has two problems.

  1/ if the time-of-day clock has gone bacwards, some entries might not
     be purged
  2/ if a new entry is added in the same second as cache_purge ran, it will
     get ignored.

To resolve these issues, we set the flushtime to the maximum possible time
before calling cache_flush, and then set it back to the minimum time
afterwards.
Signed-off-by: Neil Brown <neilb@cse.unsw.edu.au>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>