nfsd4: use recall_lock for delegation hashing

nfsd4: use recall_lock for delegation hashing

commit 931ee56c67573eb4e51c8a4e78598d965b8b059e upstream.

This fixes a bug in the handling of the fi_delegations list.

nfs4_setlease does not hold the recall_lock when adding to it. The
client_mutex is held, which prevents against concurrent list changes,
but nfsd_break_deleg_cb does not hold while walking it. New delegations
could theoretically creep onto the list while we're walking it there.

Signed-off-by: Benny Halevy <bhalevy@primarydata.com>
Signed-off-by: Jeff Layton <jlayton@primarydata.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[bwh: Backported to 3.2:
 - Adjust context
 - Also remove a list_del_init() in nfs4_setlease() which would now be
   before the corresponding list_add()
 - Drop change to nfsd_find_all_delegations(), which doesn't exist]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>