nfsd: don't halt scanning the DRC LRU list when there's an RC_INPROG entry

commit 1b19453d1c6abcfa7c312ba6c9f11a277568fc94 upstream.

Currently, the DRC cache pruner will stop scanning the list when it
hits an entry that is RC_INPROG. It's possible however for a call to
take a *very* long time. In that case, we don't want it to block other
entries from being pruned if they are expired or we need to trim the
cache to get back under the limit.

Fix the DRC cache pruner to just ignore RC_INPROG entries.

Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>