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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 519BFC072A2 for ; Wed, 15 Nov 2023 22:03:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235650AbjKOWDP (ORCPT ); Wed, 15 Nov 2023 17:03:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40056 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1343795AbjKOWDL (ORCPT ); Wed, 15 Nov 2023 17:03:11 -0500 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E1A311A1 for ; Wed, 15 Nov 2023 14:03:07 -0800 (PST) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 427C5C433C7; Wed, 15 Nov 2023 22:03:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1700085787; bh=k9CQFcI8kcrniqo5/rDbHLJ0t2pNsD41OyW3+JH/kiY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=1zlUVS2e4hzDbjuP9tCXzHY+9JywTpskl/8fXrECTVG4/WmhwhzhctMun/qB3gz4V ZKXkXlDjbUzMg50wHGDj9bDkFxmTl+a1eGIH3OwEiGz/hiwucZ1Bq6hoDpVo0w7Qb7 TH02q0zuGUPTl/bUYJyJDR085sMVsugt+8Jkcxkg= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Thomas Gleixner , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Sebastian Andrzej Siewior , Sasha Levin Subject: [PATCH 5.4 053/119] sched/rt: Provide migrate_disable/enable() inlines Date: Wed, 15 Nov 2023 17:00:43 -0500 Message-ID: <20231115220134.274562896@linuxfoundation.org> X-Mailer: git-send-email 2.42.1 In-Reply-To: <20231115220132.607437515@linuxfoundation.org> References: <20231115220132.607437515@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 5.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Thomas Gleixner [ Upstream commit 66630058e56b26b3a9cf2625e250a8c592dd0207 ] Code which solely needs to prevent migration of a task uses preempt_disable()/enable() pairs. This is the only reliable way to do so as setting the task affinity to a single CPU can be undone by a setaffinity operation from a different task/process. RT provides a seperate migrate_disable/enable() mechanism which does not disable preemption to achieve the semantic requirements of a (almost) fully preemptible kernel. As it is unclear from looking at a given code path whether the intention is to disable preemption or migration, introduce migrate_disable/enable() inline functions which can be used to annotate code which merely needs to disable migration. Map them to preempt_disable/enable() for now. The RT substitution will be provided later. Code which is annotated that way documents that it has no requirement to protect against reentrancy of a preempting task. Either this is not required at all or the call sites are already serialized by other means. Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Juri Lelli Cc: Vincent Guittot Cc: Dietmar Eggemann Cc: Steven Rostedt Cc: Ben Segall Cc: Mel Gorman Cc: Sebastian Andrzej Siewior Link: https://lore.kernel.org/r/878slclv1u.fsf@nanos.tec.linutronix.de Stable-dep-of: 36c75ce3bd29 ("nd_btt: Make BTT lanes preemptible") Signed-off-by: Sasha Levin --- include/linux/preempt.h | 30 ++++++++++++++++++++++++++++++ 1 file changed, 30 insertions(+) diff --git a/include/linux/preempt.h b/include/linux/preempt.h index bbb68dba37cc8..bc3f1aecaa194 100644 --- a/include/linux/preempt.h +++ b/include/linux/preempt.h @@ -322,4 +322,34 @@ static inline void preempt_notifier_init(struct preempt_notifier *notifier, #endif +/** + * migrate_disable - Prevent migration of the current task + * + * Maps to preempt_disable() which also disables preemption. Use + * migrate_disable() to annotate that the intent is to prevent migration, + * but not necessarily preemption. + * + * Can be invoked nested like preempt_disable() and needs the corresponding + * number of migrate_enable() invocations. + */ +static __always_inline void migrate_disable(void) +{ + preempt_disable(); +} + +/** + * migrate_enable - Allow migration of the current task + * + * Counterpart to migrate_disable(). + * + * As migrate_disable() can be invoked nested, only the outermost invocation + * reenables migration. + * + * Currently mapped to preempt_enable(). + */ +static __always_inline void migrate_enable(void) +{ + preempt_enable(); +} + #endif /* __LINUX_PREEMPT_H */ -- 2.42.0