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=-6.6 required=3.0 tests=DKIMWL_WL_MED,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL 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 A1676C5DF60 for ; Thu, 7 Nov 2019 12:44:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 672262187F for ; Thu, 7 Nov 2019 12:44:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="WJ6oDskv" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388676AbfKGMoD (ORCPT ); Thu, 7 Nov 2019 07:44:03 -0500 Received: from mail-wm1-f52.google.com ([209.85.128.52]:37267 "EHLO mail-wm1-f52.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733250AbfKGMoC (ORCPT ); Thu, 7 Nov 2019 07:44:02 -0500 Received: by mail-wm1-f52.google.com with SMTP id q130so2269488wme.2 for ; Thu, 07 Nov 2019 04:44:01 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=3oXRQtCvNsyXQh21unQL/FfTiJzS75xtE8a9rWkSxQA=; b=WJ6oDskvoMm1gpMkf1mKBxE4gXipcmYsR5x9OMbPLlgkqF3O+WQkMNCMa0VNV0FwRZ J1Yp1IAULIMWVSE6RDUZjAhf/y/Rd4p8Y1V8n0y+Ku77A/79mK03NxfdFXfxGgu0oxyq +sJ0E2bxGrsz+C4/kXbnfBjRBeO2gzO9MSjxA5uvKTSj+dkpBjr2VYd+nuUC7aaJWIgb 0L4vRf2EqR/+4T9h6YsLwdHLceF2UPuhHZxWEYkTHkcDUtWKxem7BhvrRncKD92La4sX ci//6IkGLKeynWPCltqkNv7X9DqlNnNYoCwsiuNIDSqpvwfM/OYiLKPWWkcagd+3HOjG 71sw== 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=3oXRQtCvNsyXQh21unQL/FfTiJzS75xtE8a9rWkSxQA=; b=sZhlobT5ViWY1AwLyr4+eOYKrhaiedyHaYVuiw5O9oBjatRVtOEzq5pVTJPJhoTSdd jr0J1PtYeCcIvNBfOgP0F0WqOCEUny6shKP6aNEdpqGizmXAzTvryt1k8/8m8IpKOvur 0yPDyY8dtMWYoKQcxxKfgQCjkysq+VI7pseYDeGEMh7FHYHDogY+3TjGiOXwqFGeo5fn sqOUBDNi2oYCSYHSgTIQUbLZeky3EyfEeVflTMeLbAVjsHOhdDwZxdVFSu4djFsIQTTe rh46EjiNF1Aywi7YHDvwa3E2LTFX2opWcUmEvgpd/Llqw+WlkOSZfQ36ruZ+EmjhEBvA f+LA== X-Gm-Message-State: APjAAAXK+m1I9WyVM9nBIs+hOMwA18S6UJXAO0O9ZlqhyZIabAFcE87z FiDUJq/cSLDr0JASwznp86v73g== X-Google-Smtp-Source: APXvYqz3NJjXpngz22u1SKyyrajhr3OQJlGegVqsLYHnJod461QymsH1DvNgNuAxwAYexgNEDfOt3w== X-Received: by 2002:a7b:c94e:: with SMTP id i14mr2638607wml.174.1573130640313; Thu, 07 Nov 2019 04:44:00 -0800 (PST) Received: from google.com ([2a00:79e0:d:110:d6cc:2030:37c1:9964]) by smtp.gmail.com with ESMTPSA id x8sm2013832wrm.7.2019.11.07.04.43.59 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 07 Nov 2019 04:43:59 -0800 (PST) Date: Thu, 7 Nov 2019 12:43:55 +0000 From: Quentin Perret To: Valentin Schneider Cc: kernel test robot , Peter Zijlstra , Aaron Lu , Phil Auld , Julien Desfossez , Nishanth Aravamudan , LKML , Linus Torvalds , lkp@01.org Subject: Re: [sched] 10e7071b2f: BUG:kernel_NULL_pointer_dereference,address Message-ID: <20191107124355.GA161316@google.com> References: <20191107090808.GW29418@shao2-debian> <20191107120922.GA82729@google.com> <20191107121551.GB82729@google.com> <6a23a062-9b82-668d-7945-8da34f4dc5f0@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6a23a062-9b82-668d-7945-8da34f4dc5f0@arm.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 Thursday 07 Nov 2019 at 12:37:09 (+0000), Valentin Schneider wrote: > On 07/11/2019 12:15, Quentin Perret wrote: > > On Thursday 07 Nov 2019 at 12:09:22 (+0000), Quentin Perret wrote: > >> sched_move_task() follows what Peter called the 'change' pattern, so I'm > >> thinking this is most likely the same issue. Dropping the lock causes an > >> unmitigated race between sched_move_task() and pick_next_task_dl(), so > >> hilarity ensues (set_next_task() being called twice for instance). > > > > Bah, scratch that. 10e7071b2 is clearly before the pick_next_task() > > rework, so that's not it :( > > > > And besides we don't drop the lock until reaching pick_next_task_fair(), > and the splat says it died on pick_next_task_dl() which happens earlier. Right, with the rework of pick_next_task(), we would in fact drop the lock before calling pick_next_task_dl(), which would explain the issue, hence my confusion. But that doesn't apply here, so this is another problem :( Sorry for the noise, Quentin