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=-2.0 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 0F8E3C5DF64 for ; Wed, 6 Nov 2019 16:54:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CE6542187F for ; Wed, 6 Nov 2019 16:54:54 +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="jbKtM3Te" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732255AbfKFQyx (ORCPT ); Wed, 6 Nov 2019 11:54:53 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:43380 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727894AbfKFQyx (ORCPT ); Wed, 6 Nov 2019 11:54:53 -0500 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=TqFiX/TxrEBMTuixkbn/nkca9tyWxgwszGYJJ1sXL28=; b=jbKtM3TeVTPE+bUGcnH546tTM 1eQe+mbjhaiYqn6i13+odDl03kTEil1OszifDPkmh6e+9y5PI7BWus/4vgov7K2GM/DqAEDrDSQji PS81nA8H14dUCXlMSMqD1K2MJ/Nhdcz539fLOxiBkCWEM0eDY+UydhAc6wg58dbJ6rHAa5BimU514 0mYrD1Xx9Yljt0fWLx85staoIYStJ+z74rOJ8LkQiENvobS0Y8VgRs2zyK27mJPo7CIB+elSuXRJ4 GrumUiSptQmLaa2Wk8QX/BgtVJR6VrpxTTxaGjBiJLH21R/27Dl94bG0SyZYzU+A6uOPOD5Gx7wBd cqqD2ai0A==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1iSOZv-0008J4-Jb; Wed, 06 Nov 2019 16:54:43 +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 2A2B4302C0F; Wed, 6 Nov 2019 17:53:33 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 451552025EDA7; Wed, 6 Nov 2019 17:54:37 +0100 (CET) Date: Wed, 6 Nov 2019 17:54:37 +0100 From: Peter Zijlstra To: Kirill Tkhai Cc: Quentin Perret , linux-kernel@vger.kernel.org, aaron.lwe@gmail.com, valentin.schneider@arm.com, mingo@kernel.org, pauld@redhat.com, jdesfossez@digitalocean.com, naravamudan@digitalocean.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, kernel-team@android.com, john.stultz@linaro.org Subject: Re: Re: NULL pointer dereference in pick_next_task_fair Message-ID: <20191106165437.GX4114@hirez.programming.kicks-ass.net> References: <20191028174603.GA246917@google.com> <20191106120525.GX4131@hirez.programming.kicks-ass.net> <33643a5b-1b83-8605-2347-acd1aea04f93@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33643a5b-1b83-8605-2347-acd1aea04f93@virtuozzo.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 Wed, Nov 06, 2019 at 06:51:40PM +0300, Kirill Tkhai wrote: > > +#ifdef CONFIG_SMP > > + if (!rq->nr_running) { > > + /* > > + * Make sure task_on_rq_curr() fails, such that we don't do > > + * put_prev_task() + set_next_task() on this task again. > > + */ > > + prev->on_cpu = 2; > > newidle_balance(rq, rf); > > Shouldn't we restore prev->on_cpu = 1 after newidle_balance()? Can't prev > become pickable again after newidle_balance() releases rq->lock, and we > take it again, so this on_cpu == 2 never will be cleared? Indeed so.