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=-4.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED 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 A8AB0C43381 for ; Tue, 12 Mar 2019 08:59:33 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7DDBA217F4 for ; Tue, 12 Mar 2019 08:59:33 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727654AbfCLI7c convert rfc822-to-8bit (ORCPT ); Tue, 12 Mar 2019 04:59:32 -0400 Received: from ms01.santannapisa.it ([193.205.80.98]:52354 "EHLO mail.santannapisa.it" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726465AbfCLI7b (ORCPT ); Tue, 12 Mar 2019 04:59:31 -0400 X-Greylist: delayed 3601 seconds by postgrey-1.27 at vger.kernel.org; Tue, 12 Mar 2019 04:59:30 EDT Received: from [10.1.195.109] (account l.abeni@santannapisa.it HELO nowhere) by santannapisa.it (CommuniGate Pro SMTP 6.1.11) with ESMTPSA id 137197463; Tue, 12 Mar 2019 08:59:27 +0100 Date: Tue, 12 Mar 2019 08:59:22 +0100 From: luca abeni To: "chengjian (D)" Cc: "linux-kernel@vger.kernel.org" , Li Bin , "Xiexiuqi (Xie XiuQi)" , , Peter Zijlstra Subject: Re: WARN ON at kernel/sched/deadline.c task_non_contending Message-ID: <20190312085922.13895cae@nowhere> In-Reply-To: References: Organization: Scuola Superiore S.Anna X-Mailer: Claws Mail 3.16.0 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi all, On Tue, 12 Mar 2019 10:03:12 +0800 "chengjian (D)" wrote: > Hi. > > When looking to test SCHED_DEADLINE syzkaller report an warn in > task_non_contending(). I tested the mainline kernel with the C program > and captured the same call trace. [...] > diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c > index 31c050a0d0ce..d73cb033a06d 100644 > --- a/kernel/sched/deadline.c > +++ b/kernel/sched/deadline.c > @@ -252,7 +252,6 @@ static void task_non_contending(struct > task_struct *p) if (dl_entity_is_special(dl_se)) >                 return; > > -       WARN_ON(hrtimer_active(&dl_se->inactive_timer)); >         WARN_ON(dl_se->dl_non_contending); > >         zerolag_time = dl_se->deadline - > @@ -287,7 +286,9 @@ static void task_non_contending(struct > task_struct *p) } > >         dl_se->dl_non_contending = 1; > -       get_task_struct(p); > + > +       if (!hrtimer_active(&dl_se->inactive_timer)); > +               get_task_struct(p); >         hrtimer_start(timer, ns_to_ktime(zerolag_time), > HRTIMER_MODE_REL); } At a first glance, I think the patch is OK, but I need some more time to look at the details. I'll run some experiments with the reproducer, and I'll let you know my conclusions. > Did I miss something ? > > I saw it directly remove the hrtimer in hrtime_start() if hrtime is > queued, it may be unsafe here when the timer handler is running. This is probably why I added that WARN_ON()... I'll look at a possible solution. Thanks, Luca > > Help ? > > I put the syzkaller log and C demo in attachments. > > Thanks. > > >