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=-2.1 required=3.0 tests=DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS,T_DKIM_INVALID, URIBL_BLOCKED,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 8BB9FECDFB8 for ; Fri, 20 Jul 2018 08:09:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 21AF62064D for ; Fri, 20 Jul 2018 08:09:37 +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="PCeJ1Tm2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 21AF62064D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727718AbeGTI4i (ORCPT ); Fri, 20 Jul 2018 04:56:38 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:40288 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727331AbeGTI4i (ORCPT ); Fri, 20 Jul 2018 04:56:38 -0400 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=QAo3jxuYoYiQnIcEgEM3SbDs7faq4jcPRHeNvHLkE9w=; b=PCeJ1Tm2RuDvCjBwZG+zNG4O6 Cki1TgrvgxDU8QHhGiYqenfK11XwQYJadMfyG12l0cF1Dy6auHuneDcg/p9gQyj4+v3D63Y+wrVgc /X3J5+nOhrjbczo0VNRhQ+I4UyofKXHAU6j8ixGoKuDp/GHaOi/wsIL3PWkJigpH+VLXN7y5fYJz6 i1UmHi+CkBZH4g/rzpinHyIKeAErAefw9WUw3TeCQY1NyX/FdvxjZZ1aQbaOpPReR8kFNqsizK4Ms cQS731l22KIDjeQTPEPUWWe8y206yY/rWZX+6wiPxFRe3icHVzz/IOpNhF7QGe0TtZJlItJqAiXMR LKhFfGeQg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fgQTR-0003dt-AI; Fri, 20 Jul 2018 08:09:13 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 2221420289335; Fri, 20 Jul 2018 10:09:11 +0200 (CEST) Date: Fri, 20 Jul 2018 10:09:11 +0200 From: Peter Zijlstra To: Pavel Tatashin Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, linux@armlinux.org.uk, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, john.stultz@linaro.org, sboyd@codeaurora.org, x86@kernel.org, linux-kernel@vger.kernel.org, mingo@redhat.com, tglx@linutronix.de, hpa@zytor.com, douly.fnst@cn.fujitsu.com, prarit@redhat.com, feng.tang@intel.com, pmladek@suse.com, gnomes@lxorguk.ukuu.org.uk, linux-s390@vger.kernel.org, boris.ostrovsky@oracle.com, jgross@suse.com, pbonzini@redhat.com Subject: Re: [PATCH v15 23/26] sched: early boot clock Message-ID: <20180720080911.GM2494@hirez.programming.kicks-ass.net> References: <20180719205545.16512-1-pasha.tatashin@oracle.com> <20180719205545.16512-24-pasha.tatashin@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180719205545.16512-24-pasha.tatashin@oracle.com> User-Agent: Mutt/1.10.0 (2018-05-17) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jul 19, 2018 at 04:55:42PM -0400, Pavel Tatashin wrote: > diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c > index 0e9dbb2d9aea..422cd63f8f17 100644 > --- a/kernel/sched/clock.c > +++ b/kernel/sched/clock.c > @@ -202,7 +202,25 @@ static void __sched_clock_gtod_offset(void) > > void __init sched_clock_init(void) > { > + unsigned long flags; > + > + /* > + * Set __gtod_offset such that once we mark sched_clock_running, > + * sched_clock_tick() continues where sched_clock() left off. > + * > + * Even if TSC is buggered, we're still UP at this point so it > + * can't really be out of sync. > + */ > + local_irq_save(flags); > + __sched_clock_gtod_offset(); > + local_irq_restore(flags); > + > sched_clock_running = 1; > + > + /* Now that sched_clock_running is set adjust scd */ > + local_irq_save(flags); > + sched_clock_tick(); > + local_irq_restore(flags); > } Sorry, that's still wrong. Because the moment you enable sched_clock_running we need to have everything set-up for it to run. The above looks double weird because you could've just done that =1 under the same IRQ-disable section and it would've mostly been OK (except for NMIs). But the reason it's weird like that is because you're going to change it into a static key later on. The below cures things. --- Subject: sched/clock: Close a hole in sched_clock_init() All data required for the 'unstable' sched_clock must be set-up _before_ enabling it -- setting sched_clock_running. This includes the __gtod_offset but also a recent scd stamp. Make the gtod-offset update also set the csd stamp -- it requires the same two clock reads _anyway_. This doesn't hurt in the sched_clock_tick_stable() case and ensures sched_clock_init() gets everything set-up before use. Also switch to unconditional IRQ-disable/enable because the static key stuff already requires this is not ran with IRQs disabled. Signed-off-by: Peter Zijlstra (Intel) --- kernel/sched/clock.c | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/kernel/sched/clock.c b/kernel/sched/clock.c index c5c47ad3f386..811a39aca1ce 100644 --- a/kernel/sched/clock.c +++ b/kernel/sched/clock.c @@ -197,13 +197,14 @@ void clear_sched_clock_stable(void) static void __sched_clock_gtod_offset(void) { - __gtod_offset = (sched_clock() + __sched_clock_offset) - ktime_get_ns(); + struct sched_clock_data *scd = this_scd(); + + __scd_stamp(scd); + __gtod_offset = (scd->tick_raw + __sched_clock_offset) - scd->tick_gtod; } void __init sched_clock_init(void) { - unsigned long flags; - /* * Set __gtod_offset such that once we mark sched_clock_running, * sched_clock_tick() continues where sched_clock() left off. @@ -211,16 +212,11 @@ void __init sched_clock_init(void) * Even if TSC is buggered, we're still UP at this point so it * can't really be out of sync. */ - local_irq_save(flags); + local_irq_disable(); __sched_clock_gtod_offset(); - local_irq_restore(flags); + local_irq_enable(); static_branch_inc(&sched_clock_running); - - /* Now that sched_clock_running is set adjust scd */ - local_irq_save(flags); - sched_clock_tick(); - local_irq_restore(flags); } /* * We run this as late_initcall() such that it runs after all built-in drivers,