From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753517Ab1ABHW7 (ORCPT ); Sun, 2 Jan 2011 02:22:59 -0500 Received: from mail.windriver.com ([147.11.1.11]:35174 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753465Ab1ABHW4 (ORCPT ); Sun, 2 Jan 2011 02:22:56 -0500 From: Paul Gortmaker To: stable@kernel.org, linux-kernel@vger.kernel.org Cc: stable-review@kernel.org, Daniel J Blueman , "Paul E. McKenney" , Paul Gortmaker Subject: [34-longterm 092/260] rcu: apply RCU protection to wake_affine() Date: Sun, 2 Jan 2011 02:16:28 -0500 Message-Id: <1293952756-15010-93-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.7.3.3 In-Reply-To: <1293952756-15010-1-git-send-email-paul.gortmaker@windriver.com> References: <1293952756-15010-1-git-send-email-paul.gortmaker@windriver.com> X-OriginalArrivalTime: 02 Jan 2011 07:21:51.0102 (UTC) FILETIME=[B977A1E0:01CBAA4D] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Daniel J Blueman commit f3b577dec1f2ce32d2db6d2ca6badff7002512af upstream. The task_group() function returns a pointer that must be protected by either RCU, the ->alloc_lock, or the cgroup lock (see the rcu_dereference_check() in task_subsys_state(), which is invoked by task_group()). The wake_affine() function currently does none of these, which means that a concurrent update would be within its rights to free the structure returned by task_group(). Because wake_affine() uses this structure only to compute load-balancing heuristics, there is no reason to acquire either of the two locks. Therefore, this commit introduces an RCU read-side critical section that starts before the first call to task_group() and ends after the last use of the "tg" pointer returned from task_group(). Thanks to Li Zefan for pointing out the need to extend the RCU read-side critical section from that proposed by the original patch. Signed-off-by: Daniel J Blueman Signed-off-by: Paul E. McKenney Signed-off-by: Paul Gortmaker --- kernel/sched_fair.c | 2 ++ 1 files changed, 2 insertions(+), 0 deletions(-) diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c index 461d312..94993ac 100644 --- a/kernel/sched_fair.c +++ b/kernel/sched_fair.c @@ -1272,6 +1272,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) * effect of the currently running task from the load * of the current CPU: */ + rcu_read_lock(); if (sync) { tg = task_group(current); weight = current->se.load.weight; @@ -1297,6 +1298,7 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync) balanced = !this_load || 100*(this_load + effective_load(tg, this_cpu, weight, weight)) <= imbalance*(load + effective_load(tg, prev_cpu, 0, weight)); + rcu_read_unlock(); /* * If the currently running task will sleep within -- 1.7.3.3