Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755204Ab2JZARe (ORCPT ); Thu, 25 Oct 2012 20:17:34 -0400 Received: from mail.kernel.org ([198.145.19.201]:53870 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754518Ab2JZAIN (ORCPT ); Thu, 25 Oct 2012 20:08:13 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Greg Kroah-Hartman , alan@lxorguk.ukuu.org.uk, Tejun Heo , Li Zefan Subject: [ 52/85] Revert "cgroup: Drop task_lock(parent) on cgroup_fork()" Date: Thu, 25 Oct 2012 17:06:10 -0700 Message-Id: <20121026000036.356079318@linuxfoundation.org> X-Mailer: git-send-email 1.7.12.2.421.g261b511 In-Reply-To: <20121026000031.107227138@linuxfoundation.org> References: <20121026000031.107227138@linuxfoundation.org> User-Agent: quilt/0.60-2.1.2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3106 Lines: 79 3.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tejun Heo commit 9bb71308b8133d643648776243e4d5599b1c193d upstream. This reverts commit 7e381b0eb1e1a9805c37335562e8dc02e7d7848c. The commit incorrectly assumed that fork path always performed threadgroup_change_begin/end() and depended on that for synchronization against task exit and cgroup migration paths instead of explicitly grabbing task_lock(). threadgroup_change is not locked when forking a new process (as opposed to a new thread in the same process) and even if it were it wouldn't be effective as different processes use different threadgroup locks. Revert the incorrect optimization. Signed-off-by: Tejun Heo LKML-Reference: <20121008020000.GB2575@localhost> Acked-by: Li Zefan Bitterly-Acked-by: Frederic Weisbecker Signed-off-by: Greg Kroah-Hartman --- kernel/cgroup.c | 23 ++++++----------------- 1 file changed, 6 insertions(+), 17 deletions(-) --- a/kernel/cgroup.c +++ b/kernel/cgroup.c @@ -4694,31 +4694,20 @@ static const struct file_operations proc * * A pointer to the shared css_set was automatically copied in * fork.c by dup_task_struct(). However, we ignore that copy, since - * it was not made under the protection of RCU, cgroup_mutex or - * threadgroup_change_begin(), so it might no longer be a valid - * cgroup pointer. cgroup_attach_task() might have already changed - * current->cgroups, allowing the previously referenced cgroup - * group to be removed and freed. - * - * Outside the pointer validity we also need to process the css_set - * inheritance between threadgoup_change_begin() and - * threadgoup_change_end(), this way there is no leak in any process - * wide migration performed by cgroup_attach_proc() that could otherwise - * miss a thread because it is too early or too late in the fork stage. + * it was not made under the protection of RCU or cgroup_mutex, so + * might no longer be a valid cgroup pointer. cgroup_attach_task() might + * have already changed current->cgroups, allowing the previously + * referenced cgroup group to be removed and freed. * * At the point that cgroup_fork() is called, 'current' is the parent * task, and the passed argument 'child' points to the child task. */ void cgroup_fork(struct task_struct *child) { - /* - * We don't need to task_lock() current because current->cgroups - * can't be changed concurrently here. The parent obviously hasn't - * exited and called cgroup_exit(), and we are synchronized against - * cgroup migration through threadgroup_change_begin(). - */ + task_lock(current); child->cgroups = current->cgroups; get_css_set(child->cgroups); + task_unlock(current); INIT_LIST_HEAD(&child->cg_list); } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/