NFSv4: Don't report revoked delegations as valid in nfs_have_delegation()

If the delegation is revoked, then it can't be used for caching.

Fixes: 869f9dfa4d6d ("NFSv4: Fix races between nfs_remove_bad_delegation()...")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
Cc: stable@vger.kernel.org # v3.19+
Tested-by: Oleg Drokin <green@linuxhacker.ru>
Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>

fs/nfs/delegation.c

@@ -51,6 +51,7 @@ nfs4_do_check_delegation(struct inode *inode, fmode_t flags, bool mark)
 	rcu_read_lock();
 	delegation = rcu_dereference(NFS_I(inode)->delegation);
 	if (delegation != NULL && (delegation->type & flags) == flags &&
+	    !test_bit(NFS_DELEGATION_REVOKED, &delegation->flags) &&
 	    !test_bit(NFS_DELEGATION_RETURNING, &delegation->flags)) {
 		if (mark)
 			nfs_mark_delegation_referenced(delegation);