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=-16.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=unavailable 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 D63C5C4338F for ; Sat, 7 Aug 2021 00:58:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B159D60EE4 for ; Sat, 7 Aug 2021 00:58:41 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229875AbhHGA6x (ORCPT ); Fri, 6 Aug 2021 20:58:53 -0400 Received: from foss.arm.com ([217.140.110.172]:42778 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229758AbhHGA6w (ORCPT ); Fri, 6 Aug 2021 20:58:52 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 12ABE113E; Fri, 6 Aug 2021 17:58:36 -0700 (PDT) Received: from e113632-lin.cambridge.arm.com (e113632-lin.cambridge.arm.com [10.1.194.46]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 3353F3F66F; Fri, 6 Aug 2021 17:58:33 -0700 (PDT) From: Valentin Schneider To: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org, linux-rt-users@vger.kernel.org Cc: Catalin Marinas , Will Deacon , Ingo Molnar , Peter Zijlstra , Thomas Gleixner , Steven Rostedt , Daniel Bristot de Oliveira , Sebastian Andrzej Siewior , "Paul E. McKenney" , Frederic Weisbecker , Josh Triplett , Mathieu Desnoyers , Davidlohr Bueso , Lai Jiangshan , Joel Fernandes , Anshuman Khandual , Vincenzo Frascino , Steven Price , Ard Biesheuvel Subject: [PATCH v2 2/4] sched: Introduce is_pcpu_safe() Date: Sat, 7 Aug 2021 01:58:05 +0100 Message-Id: <20210807005807.1083943-3-valentin.schneider@arm.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210807005807.1083943-1-valentin.schneider@arm.com> References: <20210807005807.1083943-1-valentin.schneider@arm.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Some areas use preempt_disable() + preempt_enable() to safely access per-CPU data. The PREEMPT_RT folks have shown this can also be done by keeping preemption enabled and instead disabling migration (and acquiring a sleepable lock, if relevant). Introduce a helper which checks whether the current task can safely access per-CPU data, IOW if the task's context guarantees the accesses will target a single CPU. This accounts for preemption, CPU affinity, and migrate disable - note that the CPU affinity check also mandates the presence of PF_NO_SETAFFINITY, as otherwise userspace could concurrently render the upcoming per-CPU access(es) unsafe. Signed-off-by: Valentin Schneider --- include/linux/sched.h | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/include/linux/sched.h b/include/linux/sched.h index debc960f41e3..b77d65f677f6 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1715,6 +1715,16 @@ static inline bool is_percpu_thread(void) #endif } +/* Is the current task guaranteed not to be migrated elsewhere? */ +static inline bool is_pcpu_safe(void) +{ +#ifdef CONFIG_SMP + return !preemptible() || is_percpu_thread() || current->migration_disabled; +#else + return true; +#endif +} + /* Per-process atomic flags. */ #define PFA_NO_NEW_PRIVS 0 /* May not gain new privileges. */ #define PFA_SPREAD_PAGE 1 /* Spread page cache over cpuset */ -- 2.25.1