smb: client: fix potential race in cifs_put_tcon()

commit c32b624 upstream.

dfs_cache_refresh() delayed worker could race with cifs_put_tcon(), so
make sure to call list_replace_init() on @tcon->dfs_ses_list after
kworker is cancelled or finished.

Fixes: 4f42a8b ("smb: client: fix DFS interlink failover")
Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: Paulo Alcantara

fs/smb/client/connect.c

@@ -2557,16 +2557,14 @@ cifs_put_tcon(struct cifs_tcon *tcon, enum smb3_tcon_ref_trace trace)
 
 	list_del_init(&tcon->tcon_list);
 	tcon->status = TID_EXITING;
-#ifdef CONFIG_CIFS_DFS_UPCALL
-	list_replace_init(&tcon->dfs_ses_list, &ses_list);
-#endif
 	spin_unlock(&tcon->tc_lock);
 	spin_unlock(&cifs_tcp_ses_lock);
 
 	/* cancel polling of interfaces */
 	cancel_delayed_work_sync(&tcon->query_interfaces);
 #ifdef CONFIG_CIFS_DFS_UPCALL
 	cancel_delayed_work_sync(&tcon->dfs_cache_work);
+	list_replace_init(&tcon->dfs_ses_list, &ses_list);
 #endif
 
 	if (tcon->use_witness) {