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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,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 67C69C43387 for ; Mon, 7 Jan 2019 17:56:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3F1182070B for ; Mon, 7 Jan 2019 17:56:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727648AbfAGR4s (ORCPT ); Mon, 7 Jan 2019 12:56:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:55181 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726942AbfAGR4r (ORCPT ); Mon, 7 Jan 2019 12:56:47 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4E29CA909; Mon, 7 Jan 2019 17:56:47 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.103]) by smtp.corp.redhat.com (Postfix) with SMTP id 194CE5DE69; Mon, 7 Jan 2019 17:56:45 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 7 Jan 2019 18:56:47 +0100 (CET) Date: Mon, 7 Jan 2019 18:56:45 +0100 From: Oleg Nesterov To: Qian Cai Cc: Peter Zijlstra , Ingo Molnar , linux kernel , gkohli@codeaurora.org Subject: Re: kernel BUG at kernel/sched/core.c:3490! Message-ID: <20190107175644.GB7636@redhat.com> References: <20190107135215.GG14122@hirez.programming.kicks-ass.net> <46089f1c-ad72-c96c-2f35-c2f60e726462@lca.pw> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <46089f1c-ad72-c96c-2f35-c2f60e726462@lca.pw> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.29]); Mon, 07 Jan 2019 17:56:47 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/07, Qian Cai wrote: > > > On 1/7/19 8:52 AM, Peter Zijlstra wrote: > > On Tue, Jan 01, 2019 at 12:44:35AM -0500, Qian Cai wrote: > >> Running some mmap() workloads to put the system on low memory situation with > >> swapping and OOM, and then it trigger this BUG(), > >> > >> void __noreturn do_task_dead(void) > >> { > >> /* Causes final put_task_struct in finish_task_switch(): */ > >> set_special_state(TASK_DEAD); > >> > >> /* Tell freezer to ignore us: */ > >> current->flags |= PF_NOFREEZE; > >> > >> __schedule(false); > >> BUG(); > >> > >> /* Avoid "noreturn function does return" - but don't continue if BUG() > >> is a NOP: */ > >> for (;;) > >> cpu_relax(); > >> } > > > > This would mean that we somehow loose the TASK_DEAD state before hitting > > schedule(), but that is something that should be avoided by > > set_special_state(), which is supposed to serialize against concurrent > > wake-ups. or may be pick_next_task() somehow returns the deactivated TASK_DEAD task? > > How readily does this reproduce? > > Running LTP oom01 [1] triggered it at least once in five attempts every time so > far on v4.20+. Have not tried much on v5.0-rc1 yet. Can you add pr_crit("XXX: %ld %d\n", current->state, current->on_rq); before that BUG() and reproduce? Oleg.