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, 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 C5B5AC43334 for ; Mon, 3 Sep 2018 08:54:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 714E320645 for ; Mon, 3 Sep 2018 08:54:49 +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="ikr40iz2" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 714E320645 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 S1727352AbeICNN5 (ORCPT ); Mon, 3 Sep 2018 09:13:57 -0400 Received: from merlin.infradead.org ([205.233.59.134]:34864 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726160AbeICNN4 (ORCPT ); Mon, 3 Sep 2018 09:13:56 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.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=+Zpx/cSPEiP3ssw0Vb2g9dyiMRBRZClIJ8aUw3VU/4I=; b=ikr40iz2RIbGO3HR4CVcaU/zk O+mqyJY+vQPF4IJGzbN79rcPBdEDdXdZZtUOEBYkM7FCx17xWZY4FxQWtPnRILK4H4xQn+UQtpe/m vRs6FaybUJk18OlOjFac7M7X5jRwLyl8lYUcPP3ylvNI8oRgH4pgV+TuhyhPLuBTov4quH+Q4spSI buLgLg0GPXxtn93hmwocVjhyUQs18OQAzD2lvsmqzPImJ5sBCmpfpuvg6/HocuZgGNYT4yFptMoAZ HHeG7P+TXvdu6Xbo8IZajttyccPxkd7vcMRkcEWqQvvW5/UDdxmjZI4xE1/4dJEVG99h3yBhElMn1 ObnFQCiVA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1fwkcq-0006hg-CR; Mon, 03 Sep 2018 08:54:24 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 293EF2024EB0A; Mon, 3 Sep 2018 10:54:23 +0200 (CEST) Date: Mon, 3 Sep 2018 10:54:23 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Kevin Shanahan , Siegfried Metz , linux-kernel@vger.kernel.org, rafael.j.wysocki@intel.com, len.brown@intel.com, rjw@rjwysocki.net, diego.viola@gmail.com, rui.zhang@intel.com, viktor_jaegerskuepper@freenet.de Subject: Re: REGRESSION: boot stalls on several old dual core Intel CPUs Message-ID: <20180903085423.GU24124@hirez.programming.kicks-ass.net> References: <74c5abc8-7430-5bc9-2f8a-a2205608bee7@mailbox.org> <20180830130439.GM24082@hirez.programming.kicks-ass.net> <20180901022125.GO4941@tuon.disenchant.local> <20180903072506.GS24124@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 Mon, Sep 03, 2018 at 09:38:15AM +0200, Thomas Gleixner wrote: > On Mon, 3 Sep 2018, Peter Zijlstra wrote: > > On Sat, Sep 01, 2018 at 11:51:26AM +0930, Kevin Shanahan wrote: > > > commit 01548f4d3e8e94caf323a4f664eb347fd34a34ab > > > Author: Martin Schwidefsky > > > Date: Tue Aug 18 17:09:42 2009 +0200 > > > > > > clocksource: Avoid clocksource watchdog circular locking dependency > > > > > > stop_machine from a multithreaded workqueue is not allowed because > > > of a circular locking dependency between cpu_down and the workqueue > > > execution. Use a kernel thread to do the clocksource downgrade. > > > > I cannot find stop_machine usage there; either it went away or I need to > > like wake up. > > timekeeping_notify() which is involved in switching clock source uses stomp > machine. ARGH... OK, lemme see if I can come up with something other than endlessly spawning that kthread. A special purpose kthread_worker would make more sense than that.