From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753062AbbIRJ2N (ORCPT ); Fri, 18 Sep 2015 05:28:13 -0400 Received: from e06smtp17.uk.ibm.com ([195.75.94.113]:43409 "EHLO e06smtp17.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752188AbbIRJ2L (ORCPT ); Fri, 18 Sep 2015 05:28:11 -0400 X-Helo: d06dlp01.portsmouth.uk.ibm.com X-MailFrom: dingel@linux.vnet.ibm.com X-RcptTo: stable@vger.kernel.org From: Dominik Dingel To: Paolo Bonzini , Peter Zijlstra Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar , Tim Chen , Dominik Dingel , Subject: [PATCH] sched: access local runqueue directly in single_task_running Date: Fri, 18 Sep 2015 11:27:45 +0200 Message-Id: <1442568465-71559-1-git-send-email-dingel@linux.vnet.ibm.com> X-Mailer: git-send-email 2.3.8 X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 15091809-0029-0000-0000-000006732608 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 2ee507c47293 ("sched: Add function single_task_running to let a task check if it is the only task running on a cpu") referenced the current runqueue with the smp_processor_id. When CONFIG_DEBUG_PREEMPT is enabled, that is only allowed if preemption is disabled or the currrent task is bound to the local cpu (e.g. kernel worker). With commit f78195129963 ("kvm: add halt_poll_ns module parameter") KVM calls single_task_running. If CONFIG_DEBUG_PREEMPT is enabled that generates a lot of kernel messages. To avoid adding preemption in that cases, as it would limit the usefulness, we change single_task_running to access directly the cpu local runqueue. Cc: Tim Chen Suggested-by: Peter Zijlstra Cc: # 4.2.x Signed-off-by: Dominik Dingel --- kernel/sched/core.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 78b4bad10..5bfad0b 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2614,13 +2614,13 @@ unsigned long nr_running(void) /* * Check if only the current task is running on the cpu. + * + * Caution result is subject to time-of-check-to-time-of-use race, + * every caller is responsible to set up additional fences if necessary. */ bool single_task_running(void) { - if (cpu_rq(smp_processor_id())->nr_running == 1) - return true; - else - return false; + return raw_rq()->nr_running == 1; } EXPORT_SYMBOL(single_task_running); -- 2.3.8