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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_2 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 66DFBC5B578 for ; Mon, 1 Jul 2019 21:28:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 32701206A3 for ; Mon, 1 Jul 2019 21:28:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726930AbfGAV22 (ORCPT ); Mon, 1 Jul 2019 17:28:28 -0400 Received: from mail.kernel.org ([198.145.29.99]:53022 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726509AbfGAV22 (ORCPT ); Mon, 1 Jul 2019 17:28:28 -0400 Received: from gandalf.local.home (cpe-66-24-58-225.stny.res.rr.com [66.24.58.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 805732064A; Mon, 1 Jul 2019 21:28:26 +0000 (UTC) Date: Mon, 1 Jul 2019 17:28:25 -0400 From: Steven Rostedt To: Corey Minyard Cc: Corey Minyard , Sebastian Andrzej Siewior , linux-rt-users@vger.kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , tglx@linutronix.de Subject: Re: [PATCH RT v2] Fix a lockup in wait_for_completion() and friends Message-ID: <20190701172825.7d861e85@gandalf.local.home> In-Reply-To: <20190701171333.37cc0567@gandalf.local.home> References: <20190509193320.21105-1-minyard@acm.org> <20190510103318.6cieoifz27eph4n5@linutronix.de> <20190628214903.6f92a9ea@oasis.local.home> <20190701190949.GB4336@minyard.net> <20190701161840.1a53c9e4@gandalf.local.home> <20190701204325.GD5041@minyard.net> <20190701170602.2fdb35c2@gandalf.local.home> <20190701171333.37cc0567@gandalf.local.home> X-Mailer: Claws Mail 3.17.3 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 1 Jul 2019 17:13:33 -0400 Steven Rostedt wrote: > On Mon, 1 Jul 2019 17:06:02 -0400 > Steven Rostedt wrote: > > > On Mon, 1 Jul 2019 15:43:25 -0500 > > Corey Minyard wrote: > > > > > > > I show that patch is already applied at > > > > > > 1921ea799b7dc561c97185538100271d88ee47db > > > sched/completion: Fix a lockup in wait_for_completion() > > > > > > git describe --contains 1921ea799b7dc561c97185538100271d88ee47db > > > v4.19.37-rt20~1 > > > > > > So I'm not sure what is going on. > > > > Bah, I'm replying to the wrong commit that I'm having issues with. > > > > I searched your name to find the patch that is of trouble, and picked > > this one. > > > > I'll go find the problem patch, sorry for the noise on this one. > > > > No, I did reply to the right email, but it wasn't the top patch I was > having issues with. It was the patch I replied to: > > This change below that Sebastian marked as stable-rt is what is causing > me an issue. Not the patch that started the thread. > In fact, my system doesn't boot with this commit in 5.0-rt. If I revert 90e1b18eba2ae4a729 ("swait: Delete the task from after a wakeup occured") the machine boots again. Sebastian, I think that's a bad commit, please revert it. Thanks! -- Steve > > > > Now.. that will fix it, but I think it is also wrong. > > > > The problem being that it violates FIFO, something that might be more > > important on -RT than elsewhere. > > > > The regular wait API seems confused/inconsistent when it uses > > autoremove_wake_function and default_wake_function, which doesn't help, > > but we can easily support this with swait -- the problematic thing is > > the custom wake functions, we musn't do that. > > > > (also, mingo went and renamed a whole bunch of wait_* crap and didn't do > > the same to swait_ so now its named all different :/) > > > > Something like the below perhaps. > > > > --- > > diff --git a/include/linux/swait.h b/include/linux/swait.h > > index 73e06e9986d4..f194437ae7d2 100644 > > --- a/include/linux/swait.h > > +++ b/include/linux/swait.h > > @@ -61,11 +61,13 @@ struct swait_queue_head { > > struct swait_queue { > > struct task_struct *task; > > struct list_head task_list; > > + unsigned int remove; > > }; > > > > #define __SWAITQUEUE_INITIALIZER(name) { \ > > .task = current, \ > > .task_list = LIST_HEAD_INIT((name).task_list), \ > > + .remove = 1, \ > > } > > > > #define DECLARE_SWAITQUEUE(name) \ > > diff --git a/kernel/sched/swait.c b/kernel/sched/swait.c > > index e83a3f8449f6..86974ecbabfc 100644 > > --- a/kernel/sched/swait.c > > +++ b/kernel/sched/swait.c > > @@ -28,7 +28,8 @@ void swake_up_locked(struct swait_queue_head *q) > > > > curr = list_first_entry(&q->task_list, typeof(*curr), task_list); > > wake_up_process(curr->task); > > - list_del_init(&curr->task_list); > > + if (curr->remove) > > + list_del_init(&curr->task_list); > > } > > EXPORT_SYMBOL(swake_up_locked); > > > > @@ -57,7 +58,8 @@ void swake_up_all(struct swait_queue_head *q) > > curr = list_first_entry(&tmp, typeof(*curr), task_list); > > > > wake_up_state(curr->task, TASK_NORMAL); > > - list_del_init(&curr->task_list); > > + if (curr->remove) > > + list_del_init(&curr->task_list); > > > > if (list_empty(&tmp)) > > break; >