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=-8.4 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 3BA48C3F2D1 for ; Mon, 2 Mar 2020 13:38:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 071882187F for ; Mon, 2 Mar 2020 13:38:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="EKnzGmTc" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727933AbgCBNi6 (ORCPT ); Mon, 2 Mar 2020 08:38:58 -0500 Received: from us-smtp-delivery-1.mimecast.com ([205.139.110.120]:29257 "EHLO us-smtp-1.mimecast.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727702AbgCBNi5 (ORCPT ); Mon, 2 Mar 2020 08:38:57 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1583156336; h=from:from:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=WcFb67oME/Nc+9ZCd/PtTGStB5FdqgJ2/9cOxFkulHA=; b=EKnzGmTcg58P9Bx1dS9Nmw67tf+DaZLmqwFYMPWa+awgUaPquVfLJLoVGiIN+dMdVUX/G1 osCSuHcpNjFUe/XARth20UfTn3ggDUkuASqV1GnfLzQifmtUdtKoK0P78RGCTgsFPe8ol7 AiDZh5TyMPl0jIpaljrDlfvR5dQet6s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-354-F6dJcXFcOz2fv8P7oQrtFA-1; Mon, 02 Mar 2020 08:38:54 -0500 X-MC-Unique: F6dJcXFcOz2fv8P7oQrtFA-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 6878C8AB9E0; Mon, 2 Mar 2020 13:38:53 +0000 (UTC) Received: from localhost.localdomain (vpn2-54-46.bne.redhat.com [10.64.54.46]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 208449CA3; Mon, 2 Mar 2020 13:38:50 +0000 (UTC) Reply-To: Gavin Shan Subject: Re: [PATCH] arm64/kernel: Simplify __cpu_up() by bailing out early To: Mark Rutland Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, will@kernel.org, maz@kernel.org, shan.gavin@gmail.com References: <20200302020340.119588-1-gshan@redhat.com> <20200302122135.GB56497@lakrids.cambridge.arm.com> From: Gavin Shan Message-ID: Date: Tue, 3 Mar 2020 00:38:48 +1100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.0 MIME-Version: 1.0 In-Reply-To: <20200302122135.GB56497@lakrids.cambridge.arm.com> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/2/20 11:21 PM, Mark Rutland wrote: > On Mon, Mar 02, 2020 at 01:03:40PM +1100, Gavin Shan wrote: >> The function __cpu_up() is invoked to bring up the target CPU through >> the backend, PSCI for example. The nested if statements won't be needed >> if we bail out early on the following two conditions where the status >> won't be checked. The code looks simplified in that case. >> >> * Error returned from the backend (e.g. PSCI) >> * The target CPU has been marked as onlined >> >> Signed-off-by: Gavin Shan > > FWIW, this looks like a nice cleanup to me: > > Reviewed-by: Mark Rutland > > While this patch leaves secondary_data.{task,stack} stale on a > successful onlining, that was already the case for a timeout, and should > be fine (since the next attempt at onlining will configure those before > poking the CPU). > > Thanks, > Mark. > Thanks, Mark. Yeah, it should be fine as you said. There are something else, which might be not relevant. @secondary_data could be accessed by multiple CPUs in parallel. For example, the master CPU boots CPU#1 and timeouts to wait it to be online in 5 seconds. CPU#1 isn't necessarily stuck in somewhere. After that, CPU#2 is brought up and might be accessing @secondary_data. At this point, CPU#1 can come back to access it either. However, @secondary_data isn't valid for CPU#1 anymore. I was thinking of something to improve the situation, but not sure if it makes any sense to do so. There are several options: (1) Make @secondary_data per-cpu variable, which looks a nature way to go. (2) To shutdown the CPU on timeout. The shutdown request can be failed to be served in theory, but it seems still an improvement. Thanks, Gavin >> --- >> arch/arm64/kernel/smp.c | 79 +++++++++++++++++++---------------------- >> 1 file changed, 37 insertions(+), 42 deletions(-) >> >> diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c >> index d4ed9a19d8fe..2a9d8f39dc58 100644 >> --- a/arch/arm64/kernel/smp.c >> +++ b/arch/arm64/kernel/smp.c >> @@ -115,60 +115,55 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle) >> update_cpu_boot_status(CPU_MMU_OFF); >> __flush_dcache_area(&secondary_data, sizeof(secondary_data)); >> >> - /* >> - * Now bring the CPU into our world. >> - */ >> + /* Now bring the CPU into our world */ >> ret = boot_secondary(cpu, idle); >> - if (ret == 0) { >> - /* >> - * CPU was successfully started, wait for it to come online or >> - * time out. >> - */ >> - wait_for_completion_timeout(&cpu_running, >> - msecs_to_jiffies(5000)); >> - >> - if (!cpu_online(cpu)) { >> - pr_crit("CPU%u: failed to come online\n", cpu); >> - ret = -EIO; >> - } >> - } else { >> + if (ret) { >> pr_err("CPU%u: failed to boot: %d\n", cpu, ret); >> return ret; >> } >> >> + /* >> + * CPU was successfully started, wait for it to come online or >> + * time out. >> + */ >> + wait_for_completion_timeout(&cpu_running, >> + msecs_to_jiffies(5000)); >> + if (cpu_online(cpu)) >> + return 0; >> + >> + pr_crit("CPU%u: failed to come online\n", cpu); >> secondary_data.task = NULL; >> secondary_data.stack = NULL; >> __flush_dcache_area(&secondary_data, sizeof(secondary_data)); >> status = READ_ONCE(secondary_data.status); >> - if (ret && status) { >> - >> - if (status == CPU_MMU_OFF) >> - status = READ_ONCE(__early_cpu_boot_status); >> + if (status == CPU_MMU_OFF) >> + status = READ_ONCE(__early_cpu_boot_status); >> >> - switch (status & CPU_BOOT_STATUS_MASK) { >> - default: >> - pr_err("CPU%u: failed in unknown state : 0x%lx\n", >> - cpu, status); >> - cpus_stuck_in_kernel++; >> - break; >> - case CPU_KILL_ME: >> - if (!op_cpu_kill(cpu)) { >> - pr_crit("CPU%u: died during early boot\n", cpu); >> - break; >> - } >> - pr_crit("CPU%u: may not have shut down cleanly\n", cpu); >> - /* Fall through */ >> - case CPU_STUCK_IN_KERNEL: >> - pr_crit("CPU%u: is stuck in kernel\n", cpu); >> - if (status & CPU_STUCK_REASON_52_BIT_VA) >> - pr_crit("CPU%u: does not support 52-bit VAs\n", cpu); >> - if (status & CPU_STUCK_REASON_NO_GRAN) >> - pr_crit("CPU%u: does not support %luK granule \n", cpu, PAGE_SIZE / SZ_1K); >> - cpus_stuck_in_kernel++; >> + switch (status & CPU_BOOT_STATUS_MASK) { >> + default: >> + pr_err("CPU%u: failed in unknown state : 0x%lx\n", >> + cpu, status); >> + cpus_stuck_in_kernel++; >> + break; >> + case CPU_KILL_ME: >> + if (!op_cpu_kill(cpu)) { >> + pr_crit("CPU%u: died during early boot\n", cpu); >> break; >> - case CPU_PANIC_KERNEL: >> - panic("CPU%u detected unsupported configuration\n", cpu); >> } >> + pr_crit("CPU%u: may not have shut down cleanly\n", cpu); >> + /* Fall through */ >> + case CPU_STUCK_IN_KERNEL: >> + pr_crit("CPU%u: is stuck in kernel\n", cpu); >> + if (status & CPU_STUCK_REASON_52_BIT_VA) >> + pr_crit("CPU%u: does not support 52-bit VAs\n", cpu); >> + if (status & CPU_STUCK_REASON_NO_GRAN) { >> + pr_crit("CPU%u: does not support %luK granule\n", >> + cpu, PAGE_SIZE / SZ_1K); >> + } >> + cpus_stuck_in_kernel++; >> + break; >> + case CPU_PANIC_KERNEL: >> + panic("CPU%u detected unsupported configuration\n", cpu); >> } >> >> return ret; >> -- >> 2.23.0 >> >