NFSv4: Check for delegation validity in nfs_start_delegation_return_locked()

Check that the delegation is still attached after taking the spin lock
in nfs_start_delegation_return_locked().

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

Author: Trond Myklebust

fs/nfs/delegation.c

@@ -307,7 +307,8 @@ nfs_start_delegation_return_locked(struct nfs_inode *nfsi)
 	if (delegation == NULL)
 		goto out;
 	spin_lock(&delegation->lock);
-	if (!test_and_set_bit(NFS_DELEGATION_RETURNING, &delegation->flags)) {
+	if (delegation->inode &&
+	    !test_and_set_bit(NFS_DELEGATION_RETURNING, &delegation->flags)) {
 		clear_bit(NFS_DELEGATION_RETURN_DELAYED, &delegation->flags);
 		/* Refcount matched in nfs_end_delegation_return() */
 		ret = nfs_get_delegation(delegation);