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_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 068E5CA9EAF for ; Mon, 21 Oct 2019 12:42:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CCB3120873 for ; Mon, 21 Oct 2019 12:42:24 +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="n9kwZPMr" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728655AbfJUMmX (ORCPT ); Mon, 21 Oct 2019 08:42:23 -0400 Received: from merlin.infradead.org ([205.233.59.134]:55838 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727959AbfJUMmX (ORCPT ); Mon, 21 Oct 2019 08:42:23 -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=s6bPfILtf/MtKzudVEW8etD9Dr+AOkV83tWje6slQZA=; b=n9kwZPMrRM8Hx1isbSoM1vlol BlzsP3wa2Ln2jzxT1cWL8TqPw3j4wXPVbklxZscTIaOg02So/jnWlwv9z9fVpHH2ZriM8ViTGVmNR C8jcDmhg23zohFfq24ziyEo1RiZeDhce+MSNBAN7h+/WSjZPO+cH4PSoJMLQAoFSQ93EVm3g7h5Jz KV1adJnkcCwf5W08oyJ+Bo42N0MA0mVI68btYI+XYDkq9gvU9yYUBgg4YIPJtWFYar2PAvMuPhiWj BQBKFoLgdQADpzd4pVUmHT6ue8r4yDbwYqxwP7K0bv4AU4yFFJuLETdlyYYUFp9MT5u6qmvRzLSK2 fANOhj4lg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iMX0p-0004V0-Rw; Mon, 21 Oct 2019 12:42:16 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 7BAAE301124; Mon, 21 Oct 2019 14:41:17 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 55BEF2022BA17; Mon, 21 Oct 2019 14:42:14 +0200 (CEST) Date: Mon, 21 Oct 2019 14:42:14 +0200 From: Peter Zijlstra To: Petr Mladek Cc: Thomas Gleixner , Ingo Molnar , Laurence Oberman , Vincent Whitchurch , Michal Hocko , linux-kernel@vger.kernel.org Subject: Re: [PATCH 1/3] watchdog/softlockup: Preserve original timestamp when touching watchdog externally Message-ID: <20191021124214.GD1817@hirez.programming.kicks-ass.net> References: <20190819104732.20966-1-pmladek@suse.com> <20190819104732.20966-2-pmladek@suse.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190819104732.20966-2-pmladek@suse.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Aug 19, 2019 at 12:47:30PM +0200, Petr Mladek wrote: > Some bug report included the same softlockups in flush_tlb_kernel_range() > in regular intervals. Unfortunately was not clear if there was a progress > or not. > > The situation can be simulated with a simply busy loop: > > while (true) > cpu_relax(); > > The softlockup detector produces: > > [ 168.277520] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] > [ 196.277604] watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [cat:4865] > [ 236.277522] watchdog: BUG: soft lockup - CPU#1 stuck for 23s! [cat:4865] > > One would expect only one softlockup report or several reports with > an increased duration. Let's just say our expectations differ. > The result is that each softlockup is reported only once unless > another process get scheduled: > > [ 320.248948] watchdog: BUG: soft lockup - CPU#2 stuck for 26s! [cat:4916] Which would greatly confuse me; as the above would have me think the situation got resolved (no more lockups reported) even though it is still very much stuck there. IOW, I don't see how this makes anything better. You're removing information.