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=-17.4 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 435AAC432BE for ; Sat, 7 Aug 2021 01:00:44 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 0A0F561186 for ; Sat, 7 Aug 2021 01:00:43 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 0A0F561186 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-Id:Date:Subject:Cc:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=+X7MsKm5xlB5yxLtoEp4OxORIRgxp3boDEiSheV1kSE=; b=4JcWguHn7LezAE +skl977QyZToyGj4LUr96cuWgPIO4wNpHw46oa5X1u05R0OxhQraJIUHoNP7inP5BhjnqZPyftZUZ YeFcRCb+ti5ZvOnNZztx1Jv4UhevGlFZIcRshiEKNJ/mjvcxo3W4Ym4yXq3ho12Su0ZbbYuSbnOQB pzUMZ7b5kxwUCmi74YrEVH124r0M2DEZayAKB2B4QK3xi9+P9w18741tvdWVhIHJoZ8GLiVy4OxGc hnmq5APFKMPFIoyP28ySPgnyeXJiprWEQs679c02dUYCzXZeKUABFUKsmiIwtHpbiKR+iq6j0dzT3 2ZTXng+7q3tGZenxHPPg==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mCAg0-00DwXM-1n; Sat, 07 Aug 2021 00:59:00 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mCAfe-00DwTR-R3 for linux-arm-kernel@lists.infradead.org; Sat, 07 Aug 2021 00:58:40 +0000 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 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210806_175838_972445_0794D515 X-CRM114-Status: GOOD ( 10.33 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.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 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel