NFSv4.1: nfs4_fl_prepare_ds - fix bugs when the connect attempt fails

- Fix an Oops when nfs4_ds_connect() returns an error.
- Always check the device status after waiting for a connect to complete.

Reported-by: Andy Adamson <andros@netapp.com>
Reported-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
Cc: <stable@vger.kernel.org> # v3.10+

fs/nfs/nfs4filelayoutdev.c

@@ -801,34 +801,34 @@ nfs4_fl_prepare_ds(struct pnfs_layout_segment *lseg, u32 ds_idx)
 	struct nfs4_file_layout_dsaddr *dsaddr = FILELAYOUT_LSEG(lseg)->dsaddr;
 	struct nfs4_pnfs_ds *ds = dsaddr->ds_list[ds_idx];
 	struct nfs4_deviceid_node *devid = FILELAYOUT_DEVID_NODE(lseg);
-
-	if (filelayout_test_devid_unavailable(devid))
-		return NULL;
+	struct nfs4_pnfs_ds *ret = ds;
 
 	if (ds == NULL) {
 		printk(KERN_ERR "NFS: %s: No data server for offset index %d\n",
 			__func__, ds_idx);
 		filelayout_mark_devid_invalid(devid);
-		return NULL;
+		goto out;
 	}
 	if (ds->ds_clp)
-		return ds;
+		goto out_test_devid;
 
 	if (test_and_set_bit(NFS4DS_CONNECTING, &ds->ds_state) == 0) {
 		struct nfs_server *s = NFS_SERVER(lseg->pls_layout->plh_inode);
 		int err;
 
 		err = nfs4_ds_connect(s, ds);
-		if (err) {
+		if (err)
 			nfs4_mark_deviceid_unavailable(devid);
-			ds = NULL;
-		}
 		nfs4_clear_ds_conn_bit(ds);
 	} else {
 		/* Either ds is connected, or ds is NULL */
 		nfs4_wait_ds_connect(ds);
 	}
-	return ds;
+out_test_devid:
+	if (filelayout_test_devid_unavailable(devid))
+		ret = NULL;
+out:
+	return ret;
 }
 
 module_param(dataserver_retrans, uint, 0644);