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 943C1C5DF62 for ; Wed, 6 Nov 2019 13:08:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 6184A217F4 for ; Wed, 6 Nov 2019 13:08:53 +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="gg0JNqLU" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731486AbfKFNIw (ORCPT ); Wed, 6 Nov 2019 08:08:52 -0500 Received: from bombadil.infradead.org ([198.137.202.133]:33212 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726781AbfKFNIw (ORCPT ); Wed, 6 Nov 2019 08:08:52 -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=ysmyeQuCWUxR2JMbHNgT/a1i2tmoz69jj5TSgPi059w=; b=gg0JNqLU0+0XO29H1NTao9AwR EtbjuUKLk7Bfv63FAk0Ee2s9c13LIdmL6/jZtuUqt1KeiFgKrc/cGzgz6N4vfeIaJ8z3wJGitrRaR CR5UlhdjtlyFsTD9f8DjCpuaOnF7soZdzKTPZkZfazcK/1b7H7DeBehZFPtfFWYTkIBfJ6269TLar iqbfeVwNckDtMvRZEhg56OmLxCdnGs0MtaQuW1xZBsJnn3yOmG9zTB+lMlCkhyej8mQKlsA20FkL0 eRtZaDXtBEJ8AMD4xtTETSF5EYb22hzjTSVIVT8RK1C2La5IuIBDPxipU/WfckuHmuE9lAkVB2UOT ZNoJA8XGg==; 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 1iSL3B-0004uR-9W; Wed, 06 Nov 2019 13:08:41 +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 8F740300692; Wed, 6 Nov 2019 14:07:34 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id A4AAB2025EDA2; Wed, 6 Nov 2019 14:08:38 +0100 (CET) Date: Wed, 6 Nov 2019 14:08:38 +0100 From: Peter Zijlstra To: Quentin Perret Cc: 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: NULL pointer dereference in pick_next_task_fair Message-ID: <20191106130838.GL5671@hirez.programming.kicks-ass.net> References: <20191028174603.GA246917@google.com> <20191106120525.GX4131@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191106120525.GX4131@hirez.programming.kicks-ass.net> 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 01:05:25PM +0100, Peter Zijlstra wrote: > On Mon, Oct 28, 2019 at 05:46:03PM +0000, Quentin Perret wrote: > > > > After digging a bit, the offending commit seems to be: > > > > 67692435c411 ("sched: Rework pick_next_task() slow-path") > > > > By 'offending' I mean that reverting it makes the issue go away. The > > issue comes from the fact that pick_next_entity() returns a NULL se in > > the 'simple' path of pick_next_task_fair(), which causes obvious > > problems in the subsequent call to set_next_entity(). > > > > I'll dig more, but if anybody understands the issue in the meatime feel > > free to send me a patch to try out :) > > So for all those who didn't follow along on IRC, the below seems to cure > things. > > The only thing I'm now considering is if we shouldn't be setting > ->on_cpu=2 _before_ calling put_prev_task(). I'll go audit the RT/DL > cases. So I think it all works, but that's more by accident than anything else. I'll move the ->on_cpu=2 assignment earlier. That clearly avoids calling put_prev_task() while we're in put_prev_task().