From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756048AbYLJXdZ (ORCPT ); Wed, 10 Dec 2008 18:33:25 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754554AbYLJXdQ (ORCPT ); Wed, 10 Dec 2008 18:33:16 -0500 Received: from smtp-out.google.com ([216.239.45.13]:17412 "EHLO smtp-out.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754011AbYLJXdP (ORCPT ); Wed, 10 Dec 2008 18:33:15 -0500 DomainKey-Signature: a=rsa-sha1; s=beta; d=google.com; c=nofws; q=dns; h=mime-version:date:message-id:subject:from:to:content-type:content-transfer-encoding; b=Pahi34OjzuyOcKxtZUlRHcu4aVYVgt0YYVa0aK1nVjhLN0VTWQkl2ICwUNIeCEc8B wIFfuYiEuSj5AQ4yqic+Q== MIME-Version: 1.0 Date: Wed, 10 Dec 2008 15:33:12 -0800 Message-ID: <6599ad830812101533r6cb007eeu5ef19499e278f6b7@mail.gmail.com> Subject: [PATCH] CGroups: Fix a race between rmdir and remount From: Paul Menage To: Andrew Morton , Linux Containers , LKML Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Fix a race between rmdir and remount When a cgroup is removed, it's unlinked from its parent's children list, but not actually freed until the last dentry on it is released (at which point cgrp->root->number_of_cgroups is decremented). Currently rebind_subsystems checks for the top cgroup's child list being empty in order to rebind subsystems into or out of a hierarchy - this can result in the set of subsystems bound to a hierarchy being different than the set of subsystems with state in the removed-but-not-freed cgroup. The simplest fix for this is to forbid remounts that change the set of subsystems on a hierarchy that has removed-but-not-freed cgroups. This bug can be reproduced via: mkdir /mnt/cg mount -t cgroup -o ns,freezer cgroup /mnt/cg mkdir /mnt/cg/foo sleep 1h < /mnt/cg/foo & rmdir /mnt/cg/foo mount -t cgroup -o remount,ns,devices,freezer cgroup /mnt/cg kill $! Signed-off-by: Paul Menage --- kernel/cgroup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) Index: hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c =================================================================== --- hierarchy_lock-mmotm-2008-12-09.orig/kernel/cgroup.c +++ hierarchy_lock-mmotm-2008-12-09/kernel/cgroup.c @@ -702,7 +702,7 @@ static int rebind_subsystems(struct cgro * any child cgroups exist. This is theoretically supportable * but involves complex error handling, so it's being left until * later */ - if (!list_empty(&cgrp->children)) + if (root->number_of_cgroups > 1) return -EBUSY; /* Process each subsystem */