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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 915C6ECDE44 for ; Sun, 28 Oct 2018 08:34:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3A69520831 for ; Sun, 28 Oct 2018 08:34:06 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3A69520831 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1727065AbeJ1RSC (ORCPT ); Sun, 28 Oct 2018 13:18:02 -0400 Received: from mail-wr1-f65.google.com ([209.85.221.65]:45390 "EHLO mail-wr1-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726396AbeJ1RSC (ORCPT ); Sun, 28 Oct 2018 13:18:02 -0400 Received: by mail-wr1-f65.google.com with SMTP id n5-v6so5314027wrw.12 for ; Sun, 28 Oct 2018 01:34:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=ILCb/eJh1SVgF/PZMp29WCxb/WlQZWxjcUY/KIBpTVk=; b=XCCR3dyYn2WP074IOSJwtkcrS8Wq60OCeql5RBTJW+qSaUgGH8aepsvk1dQko3Je/p rhnWKEMBqxaAZELCKYxLzUlL1/z7IWoo2+7+aExO7gkOlT5ZoklJmGWAO11RjxqhIBP8 smQWVqE4epKhMY6SuIkCWMxIOyV7tj2QbKz+95QMPwrUrRB3TGK76lS3tahXkdBgDHkz DJaWWwcVPDLqp8WGd7ZNVOb9K5PpAEEpw1oQAVBy/GdBs+G2vFDF3iUNZwr7JPxIm1Ih GS9pQxIboG3kzx6ywr0cp1s9mSUi/z0fHrx3fWr0aSUf+tY6JquGFf0TLnl6TGGYS44V XxTA== X-Gm-Message-State: AGRZ1gIvL7IGFjamWWgoPVyt6WPah4pW3Ef60vbLgN/kLZVptB52Ergq VG7lyvRsYIFbHgaB0nJANJsqKQ== X-Google-Smtp-Source: AJdET5dxHKeh9gTGp0GijX2TnvX3+rOK1YMYn9bGYFrVE/c19izlm9tPb2ciZGFPf1t+Do6FMruXeA== X-Received: by 2002:adf:8304:: with SMTP id 4-v6mr10722487wrd.285.1540715642118; Sun, 28 Oct 2018 01:34:02 -0700 (PDT) Received: from localhost.localdomain ([151.35.247.48]) by smtp.gmail.com with ESMTPSA id c9-v6sm11942692wrh.50.2018.10.28.01.33.58 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Sun, 28 Oct 2018 01:34:01 -0700 (PDT) Date: Sun, 28 Oct 2018 09:33:55 +0100 From: Juri Lelli To: Dmitry Vyukov Cc: Peter Zijlstra , luca abeni , Thomas Gleixner , Juri Lelli , syzbot , Borislav Petkov , "H. Peter Anvin" , LKML , Ingo Molnar , nstange@suse.de, syzkaller-bugs@googlegroups.com, henrik@austad.us, Tommaso Cucinotta , Claudio Scordino , Daniel Bristot de Oliveira Subject: Re: INFO: rcu detected stall in do_idle Message-ID: <20181028083355.GA30631@localhost.localdomain> References: <20181016153608.GH9130@localhost.localdomain> <20181018082838.GA21611@localhost.localdomain> <20181018122331.50ed3212@luca64> <20181018104713.GC21611@localhost.localdomain> <20181018130811.61337932@luca64> <20181019113942.GH3121@hirez.programming.kicks-ass.net> <20181019225005.61707c64@nowhere> <20181024120335.GE29272@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: 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 27/10/18 12:16, Dmitry Vyukov wrote: > On Wed, Oct 24, 2018 at 1:03 PM, Juri Lelli wrote: > > > > On 19/10/18 22:50, luca abeni wrote: > > > On Fri, 19 Oct 2018 13:39:42 +0200 > > > Peter Zijlstra wrote: > > > > > > > On Thu, Oct 18, 2018 at 01:08:11PM +0200, luca abeni wrote: > > > > > Ok, I see the issue now: the problem is that the "while > > > > > (dl_se->runtime <= 0)" loop is executed at replenishment time, but > > > > > the deadline should be postponed at enforcement time. > > > > > > > > > > I mean: in update_curr_dl() we do: > > > > > dl_se->runtime -= scaled_delta_exec; > > > > > if (dl_runtime_exceeded(dl_se) || dl_se->dl_yielded) { > > > > > ... > > > > > enqueue replenishment timer at dl_next_period(dl_se) > > > > > But dl_next_period() is based on a "wrong" deadline! > > > > > > > > > > > > > > > I think that inserting a > > > > > while (dl_se->runtime <= -pi_se->dl_runtime) { > > > > > dl_se->deadline += pi_se->dl_period; > > > > > dl_se->runtime += pi_se->dl_runtime; > > > > > } > > > > > immediately after "dl_se->runtime -= scaled_delta_exec;" would fix > > > > > the problem, no? > > > > > > > > That certainly makes sense to me. > > > > > > Good; I'll try to work on this idea in the weekend. > > > > So, we (me and Luca) managed to spend some more time on this and found a > > few more things worth sharing. I'll try to summarize what we have got so > > far (including what already discussed) because impression is that each > > point might deserve a fix or at least consideration (just amazing how a > > simple random fuzzer thing can highlight all that :). > > 1. Fuzzing finds bugs in any code. Always. > If a code wasn't fuzzed, there are bugs. > > 2. This fuzzer is not so simple ;) Indeed! I meant that it's amazing how the fuzzer was able to forge a relatively simple reproducer that highlighted the problem.