Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758975AbZCWQDa (ORCPT ); Mon, 23 Mar 2009 12:03:30 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758202AbZCWQBR (ORCPT ); Mon, 23 Mar 2009 12:01:17 -0400 Received: from hera.kernel.org ([140.211.167.34]:59391 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759410AbZCWQBI (ORCPT ); Mon, 23 Mar 2009 12:01:08 -0400 Date: Mon, 23 Mar 2009 15:57:45 GMT From: Bharata B Rao To: linux-tip-commits@vger.kernel.org Cc: linux-kernel@vger.kernel.org, hpa@zytor.com, mingo@redhat.com, a.p.zijlstra@chello.nl, lizf@cn.fujitsu.com, menage@google.com, dhaval@linux.vnet.ibm.com, balbir@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com, tglx@linutronix.de, kamezawa.hiroyu@jp.fujitsu.com, mingo@elte.hu Reply-To: mingo@redhat.com, hpa@zytor.com, linux-kernel@vger.kernel.org, lizf@cn.fujitsu.com, a.p.zijlstra@chello.nl, dhaval@linux.vnet.ibm.com, menage@google.com, balbir@linux.vnet.ibm.com, bharata@linux.vnet.ibm.com, tglx@linutronix.de, kamezawa.hiroyu@jp.fujitsu.com, mingo@elte.hu In-Reply-To: <20090323043253.GA3306@in.ibm.com> References: <20090323043253.GA3306@in.ibm.com> Subject: [tip:core/percpu] cpuacct: make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used -v2 Message-ID: Git-Commit-ID: 0d8ba94c48dc07d1c47f18b24826cbafcc4d7282 X-Mailer: tip-git-log-daemon MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.0 (hera.kernel.org [127.0.0.1]); Mon, 23 Mar 2009 15:57:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2499 Lines: 70 Commit-ID: 0d8ba94c48dc07d1c47f18b24826cbafcc4d7282 Gitweb: http://git.kernel.org/tip/0d8ba94c48dc07d1c47f18b24826cbafcc4d7282 Author: Bharata B Rao AuthorDate: Mon, 23 Mar 2009 10:02:53 +0530 Committer: Ingo Molnar CommitDate: Mon, 23 Mar 2009 16:55:26 +0100 cpuacct: make cpuacct hierarchy walk in cpuacct_charge() safe when rcupreempt is used -v2 Impact: fix cgroups race under rcu-preempt cpuacct_charge() obtains task's ca and does a hierarchy walk upwards. This can race with the task's movement between cgroups. This race can cause an access to freed ca pointer in cpuacct_charge() or access to invalid cgroups pointer of the task. This will not happen with rcu or tree rcu as cpuacct_charge() is called with preemption disabled. However if rcupreempt is used, the race is seen. Thanks to Li Zefan for explaining this. Fix this race by explicitly protecting ca and the hierarchy walk with rcu_read_lock(). Changes for v2: - Update patch descrition (as per Li Zefan's review comments). - Remove comments in cpuacct_charge() which explained why rcu_read_lock() was needed (as per Peter Zijlstra's review comments). Signed-off-by: Bharata B Rao Cc: Dhaval Giani Cc: Li Zefan Cc: Paul Menage Cc: KAMEZAWA Hiroyuki Acked-by: Peter Zijlstra Acked-by: Balbir Singh Tested-by: Balbir Singh LKML-Reference: <20090323043253.GA3306@in.ibm.com> Signed-off-by: Ingo Molnar --- kernel/sched.c | 3 +++ 1 files changed, 3 insertions(+), 0 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index 61e6356..ebadc7a 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -9597,6 +9597,8 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime) return; cpu = task_cpu(tsk); + + rcu_read_lock(); ca = task_ca(tsk); do { @@ -9604,6 +9606,7 @@ static void cpuacct_charge(struct task_struct *tsk, u64 cputime) *cpuusage += cputime; ca = ca->parent; } while (ca); + rcu_read_unlock(); } struct cgroup_subsys cpuacct_subsys = { -- 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/