From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_NEOMUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8A904C6778C for ; Thu, 5 Jul 2018 15:50:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3546921A3A for ; Thu, 5 Jul 2018 15:50:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3546921A3A Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754042AbeGEPun (ORCPT ); Thu, 5 Jul 2018 11:50:43 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:50994 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753859AbeGEPul (ORCPT ); Thu, 5 Jul 2018 11:50:41 -0400 Received: from bigeasy by Galois.linutronix.de with local (Exim 4.80) (envelope-from ) id 1fb6Wg-0006Pd-Ub; Thu, 05 Jul 2018 17:50:35 +0200 Date: Thu, 5 Jul 2018 17:50:34 +0200 From: Sebastian Andrzej Siewior To: Joe Korty Cc: Julia Cartwright , tglx@linutronix.de, rostedt@goodmis.org, linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH RT] sched/migrate_disable: fallback to preempt_disable() instead barrier() Message-ID: <20180705155034.s6q2lsqc3o7srzwp@linutronix.de> References: <20180704173519.GA24614@zipoli.concurrent-rt.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180704173519.GA24614@zipoli.concurrent-rt.com> User-Agent: NeoMutt/20180512 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org migrate_disable() does nothing !SMP && !RT. This is bad for two reasons: - The futex code relies on the fact migrate_disable() is part of spin_lock(). There is a workaround for the !in_atomic() case in migrate_disable() which work-arounds the different ordering (non-atomic lock and atomic unlock). - we have a few instances where preempt_disable() is replaced with migrate_disable(). For both cases it is bad if migrate_disable() ends up as barrier() instead of preempt_disable(). Let migrate_disable() fallback to preempt_disable(). Cc: stable-rt@vger.kernel.org Reported-by: joe.korty@concurrent-rt.com Signed-off-by: Sebastian Andrzej Siewior --- include/linux/preempt.h | 4 ++-- kernel/sched/core.c | 2 ++ 2 files changed, 4 insertions(+), 2 deletions(-) diff --git a/include/linux/preempt.h b/include/linux/preempt.h index 043e431a7e8e..d46688d521e6 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -241,8 +241,8 @@ static inline int __migrate_disabled(struct task_struct *p) } #else -#define migrate_disable() barrier() -#define migrate_enable() barrier() +#define migrate_disable() preempt_disable() +#define migrate_enable() preempt_enable() static inline int __migrate_disabled(struct task_struct *p) { return 0; diff --git a/kernel/sched/core.c b/kernel/sched/core.c index ac3fb8495bd5..626a62218518 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -7326,6 +7326,7 @@ void migrate_disable(void) #endif p->migrate_disable++; + preempt_disable(); } EXPORT_SYMBOL(migrate_disable); @@ -7349,6 +7350,7 @@ void migrate_enable(void) WARN_ON_ONCE(p->migrate_disable <= 0); p->migrate_disable--; + preempt_enable(); } EXPORT_SYMBOL(migrate_enable); #endif -- 2.18.0