From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755016AbZLIKPX (ORCPT ); Wed, 9 Dec 2009 05:15:23 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754591AbZLIKPU (ORCPT ); Wed, 9 Dec 2009 05:15:20 -0500 Received: from www.tglx.de ([62.245.132.106]:40004 "EHLO www.tglx.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754117AbZLIKPL (ORCPT ); Wed, 9 Dec 2009 05:15:11 -0500 Message-Id: <20091209100706.789059966@linutronix.de> User-Agent: quilt/0.47-1 Date: Wed, 09 Dec 2009 10:15:01 -0000 From: Thomas Gleixner To: LKML Cc: Ingo Molnar , Peter Zijlstra Subject: [patch 2/4] sched: Use rcu in sched_get/set_affinity() References: <20091209100540.511353305@linutronix.de> Content-Disposition: inline; filename=sched-use-rcu-in-affinity-get-set.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org tasklist_lock is held read locked to protect the find_task_by_vpid() call and to prevent the task going away. sched_setaffinity acquires a task struct ref and drops tasklist lock right away. The access to the cpus_allowed mask is protected by rq->lock. rcu_read_lock() provides the same protection here. Signed-off-by: Thomas Gleixner --- kernel/sched.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) Index: linux-2.6-tip/kernel/sched.c =================================================================== --- linux-2.6-tip.orig/kernel/sched.c +++ linux-2.6-tip/kernel/sched.c @@ -6535,22 +6535,18 @@ long sched_setaffinity(pid_t pid, const int retval; get_online_cpus(); - read_lock(&tasklist_lock); + rcu_read_lock(); p = find_process_by_pid(pid); if (!p) { - read_unlock(&tasklist_lock); + rcu_read_unlock(); put_online_cpus(); return -ESRCH; } - /* - * It is not safe to call set_cpus_allowed with the - * tasklist_lock held. We will bump the task_struct's - * usage count and then drop tasklist_lock. - */ + /* Prevent p going away */ get_task_struct(p); - read_unlock(&tasklist_lock); + rcu_read_unlock(); if (!alloc_cpumask_var(&cpus_allowed, GFP_KERNEL)) { retval = -ENOMEM; @@ -6636,7 +6632,7 @@ long sched_getaffinity(pid_t pid, struct int retval; get_online_cpus(); - read_lock(&tasklist_lock); + rcu_read_lock(); retval = -ESRCH; p = find_process_by_pid(pid); @@ -6652,7 +6648,7 @@ long sched_getaffinity(pid_t pid, struct task_rq_unlock(rq, &flags); out_unlock: - read_unlock(&tasklist_lock); + rcu_read_unlock(); put_online_cpus(); return retval;