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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 1D815C43387 for ; Fri, 18 Jan 2019 07:20:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D577D20855 for ; Fri, 18 Jan 2019 07:20:52 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="bqy0cdFY" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727430AbfARHUv (ORCPT ); Fri, 18 Jan 2019 02:20:51 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:43608 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727279AbfARHUu (ORCPT ); Fri, 18 Jan 2019 02:20:50 -0500 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=M0/OiNC9ecv0z60I4ZUNlIm8L/rcWMOBU38ZVDfxiG8=; b=bqy0cdFYLnVOFhtZAHSGm5Aud tQreOmoN3PM83is+L1iyRnihnu/BYH1YhnyNbre21u57ZEUgI4eMwRaTAx1oh14P0U4NqTsKshQbn SEYuUtrFJFzduckHcAKEvWwYAJSOB6HvQjI6FuiD/upbzBqzqqG73aRrRTqd2qOzIah0F/AnGfwJT +u0Gni9DZL/S8CFAOt8xNo+QOMHNuE7VPv7C1BvYZ8p7GQ0EofOS+D1gCficuZohYUL0s7VyzcRyr 7jPKcEdD3mzXSQ4Ns6me7WKuqgeTiqxoVR1Os1uQCngiy3lOa1NC5Z7TCu2pXQk6ravkwSmjgDToc G6H+pA+/g==; Received: from hch by bombadil.infradead.org with local (Exim 4.90_1 #2 (Red Hat Linux)) id 1gkOSF-0003Lt-1t; Fri, 18 Jan 2019 07:20:39 +0000 Date: Thu, 17 Jan 2019 23:20:38 -0800 From: Christoph Hellwig To: Atish Patra Cc: Christoph Hellwig , Patrick =?iso-8859-1?Q?St=E4hlin?= , Albert Ou , Jason Cooper , Alan Kao , Dmitriy Cherkasov , Anup Patel , Daniel Lezcano , "linux-kernel@vger.kernel.org" , Michael Clark , Marc Zyngier , Palmer Dabbelt , Andreas Schwab , "linux-riscv@lists.infradead.org" , Thomas Gleixner , Zong Li Subject: Re: [PATCH v2 1/8] RISC-V: Do not wait indefinitely in __cpu_up Message-ID: <20190118072038.GA5171@infradead.org> References: <1546940318-9752-1-git-send-email-atish.patra@wdc.com> <1546940318-9752-2-git-send-email-atish.patra@wdc.com> <20190115135125.GA28946@infradead.org> <1995e941-a8cf-c12e-71ae-7b50cf6c0ca5@wdc.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1995e941-a8cf-c12e-71ae-7b50cf6c0ca5@wdc.com> User-Agent: Mutt/1.9.2 (2017-12-15) X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 17, 2019 at 06:35:39PM -0800, Atish Patra wrote: > On 1/15/19 5:51 AM, Christoph Hellwig wrote: > > > void *__cpu_up_stack_pointer[NR_CPUS]; > > > void *__cpu_up_task_pointer[NR_CPUS]; > > > +static DECLARE_COMPLETION(cpu_running); > > > void __init smp_prepare_boot_cpu(void) > > > { > > > @@ -81,6 +82,7 @@ void __init setup_smp(void) > > > int __cpu_up(unsigned int cpu, struct task_struct *tidle) > > > { > > > + int ret = 0; > > > int hartid = cpuid_to_hartid_map(cpu); > > > tidle->thread_info.cpu = cpu; > > > @@ -96,10 +98,15 @@ int __cpu_up(unsigned int cpu, struct task_struct *tidle) > > > task_stack_page(tidle) + THREAD_SIZE); > > > WRITE_ONCE(__cpu_up_task_pointer[hartid], tidle); > > > - while (!cpu_online(cpu)) > > > - cpu_relax(); > > > + wait_for_completion_timeout(&cpu_running, > > > + msecs_to_jiffies(1000)); > > > > Having a global completion here worries me. I bet we have some higher > > level serialization, but can we comment or even better lockdep assert on > > that? > > > > Yes. It is serialized from smp.c in smp_init(). It brings one cpu online > at a time for preset_cpu mask. > > Do we still need a lockdep assert ? I guess the real lock is through cpu_hotplug_lock. And yes, a comment or even better lockdep assert would be good.