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=-9.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 674B1C3A5A2 for ; Fri, 23 Aug 2019 11:58:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 46CD622CE3 for ; Fri, 23 Aug 2019 11:58:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2393803AbfHWL62 (ORCPT ); Fri, 23 Aug 2019 07:58:28 -0400 Received: from foss.arm.com ([217.140.110.172]:32992 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389426AbfHWL6Z (ORCPT ); Fri, 23 Aug 2019 07:58:25 -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 D37C81570; Fri, 23 Aug 2019 04:58:24 -0700 (PDT) Received: from e120937-lin.cambridge.arm.com (e120937-lin.cambridge.arm.com [10.1.197.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 49F0F3F246; Fri, 23 Aug 2019 04:58:23 -0700 (PDT) From: Cristian Marussi To: linux-kernel@vger.kernel.org Cc: linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, dave.martin@arm.com, james.morse@arm.com, mark.rutland@arm.com, catalin.marinas@arm.com, will@kernel.org, tglx@linutronix.de, peterz@infradead.org, takahiro.akashi@linaro.org, hidehiro.kawai.ez@hitachi.com Subject: [RFC PATCH 1/7] smp: add generic SMP-stop support to common code Date: Fri, 23 Aug 2019 12:57:14 +0100 Message-Id: <20190823115720.605-2-cristian.marussi@arm.com> X-Mailer: git-send-email 2.17.1 In-Reply-To: <20190823115720.605-1-cristian.marussi@arm.com> References: <20190823115720.605-1-cristian.marussi@arm.com> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There was a lot of code duplication across architectures regarding the SMP stop procedures' logic; moreover some of this duplicated code logic happened to be similarly faulty across a few architectures: while fixing such logic, move such generic logic as much as possible inside common code. Collect all the common logic related to SMP stop operations into the common SMP code; any architecture willing to use such centralized logic can select CONFIG_ARCH_USE_COMMON_STOP=y and provide the related arch-specific helpers: in such a scenario, those architectures will transparently start using the common code provided by smp_send_stop() common function. On the other side, Architectures not willing to use common code SMP stop logic will simply leave CONFIG_ARCH_USE_COMMON_STOP undefined and carry on executing their local arch-specific smp_send_stop() as before. Suggested-by: Dave Martin Signed-off-by: Cristian Marussi --- include/linux/smp.h | 16 ++++++++++++ kernel/smp.c | 63 +++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 79 insertions(+) diff --git a/include/linux/smp.h b/include/linux/smp.h index 6fc856c9eda5..0fea0e6d2339 100644 --- a/include/linux/smp.h +++ b/include/linux/smp.h @@ -77,6 +77,22 @@ int smp_call_function_single_async(int cpu, call_single_data_t *csd); */ extern void smp_send_stop(void); +#ifdef CONFIG_ARCH_USE_COMMON_SMP_STOP +/* + * Any Architecture willing to use STOP common logic implementation + * MUST at least provide the arch_smp_stop_call() helper which is in + * charge of its own arch-specific CPU-stop mechanism. + */ +extern void arch_smp_stop_call(cpumask_t *cpus); + +/* + * An Architecture CAN also provide the arch_smp_cpus_stop_complete() + * dedicated helper, to perform any final arch-specific operation on + * the local CPU once the other CPUs have been successfully stopped. + */ +void arch_smp_cpus_stop_complete(void); +#endif + /* * sends a 'reschedule' event to another CPU: */ diff --git a/kernel/smp.c b/kernel/smp.c index 7dbcb402c2fc..700502ee2546 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -20,6 +20,7 @@ #include #include #include +#include #include "smpboot.h" @@ -817,3 +818,65 @@ int smp_call_on_cpu(unsigned int cpu, int (*func)(void *), void *par, bool phys) return sscs.ret; } EXPORT_SYMBOL_GPL(smp_call_on_cpu); + +#ifdef CONFIG_ARCH_USE_COMMON_SMP_STOP +void __weak arch_smp_cpus_stop_complete(void) { } + +static inline bool any_other_cpus_online(cpumask_t *mask, + unsigned int this_cpu_id) +{ + cpumask_copy(mask, cpu_online_mask); + cpumask_clear_cpu(this_cpu_id, mask); + + return !cpumask_empty(mask); +} + +/* + * This centralizes the common logic to: + * + * - evaluate which CPUs are online and needs to be notified for stop, + * while considering properly the status of the calling CPU + * + * - call the arch-specific helpers to request the effective stop + * + * - wait for the stop operation to be completed across all involved CPUs + * monitoring the cpu_online_mask + */ +void smp_send_stop(void) +{ + unsigned int this_cpu_id; + cpumask_t mask; + + this_cpu_id = smp_processor_id(); + if (any_other_cpus_online(&mask, this_cpu_id)) { + unsigned long timeout; + unsigned int this_cpu_online = cpu_online(this_cpu_id); + + if (system_state <= SYSTEM_RUNNING) + pr_crit("stopping secondary CPUs\n"); + arch_smp_stop_call(&mask); + + /* + * Wait up to one second for other CPUs to stop. + * + * Here we rely simply on cpu_online_mask to sync with + * arch-specific stop code without bloating the code with an + * additional atomic_t ad-hoc counter. + * + * As a consequence we'll need proper explicit memory barriers + * in case the other CPUs running the arch-specific stop-code + * would need to commit to memory some data (like saved_regs). + */ + timeout = USEC_PER_SEC; + while (num_online_cpus() > this_cpu_online && timeout--) + udelay(1); + /* ensure any stopping-CPUs memory access is made visible */ + smp_rmb(); + if (num_online_cpus() > this_cpu_online) + pr_warn("failed to stop secondary CPUs %*pbl\n", + cpumask_pr_args(cpu_online_mask)); + } + /* Perform final (possibly arch-specific) work on this CPU */ + arch_smp_cpus_stop_complete(); +} +#endif -- 2.17.1