From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751933Ab1I1AWx (ORCPT ); Tue, 27 Sep 2011 20:22:53 -0400 Received: from www.linutronix.de ([62.245.132.108]:57269 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751207Ab1I1AWw (ORCPT ); Tue, 27 Sep 2011 20:22:52 -0400 Date: Wed, 28 Sep 2011 02:22:49 +0200 (CEST) From: Thomas Gleixner To: Steven Rostedt cc: Tejun Heo , LKML , Peter Zijlstra Subject: Re: [PATCH] sched/kthread: Complain loudly when others violate our flags In-Reply-To: <1317158254.26514.55.camel@gandalf.stny.rr.com> Message-ID: References: <1317158254.26514.55.camel@gandalf.stny.rr.com> User-Agent: Alpine 2.02 (LFD 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1,SHORTCIRCUIT=-0.0001 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 27 Sep 2011, Steven Rostedt wrote: > I looked at the task that it tried to migrate, and it happened to be the > kworker thread! Then I went into kernel/workqueue.c and found this > nonsense: > > if (bind && !on_unbound_cpu) > kthread_bind(worker->task, gcwq->cpu); > else { > worker->task->flags |= PF_THREAD_BOUND; > if (on_unbound_cpu) > worker->flags |= WORKER_UNBOUND; > } > > Nothing but the scheduler and kthread_bind() has the right to set the > PF_THREAD_BOUND flag. Especially when the thread IS NOT BOUNDED!!!!!! Yikes, I somehow missed that gem. :( > I don't go around and stick my hand down your pants to play with your > flags! Don't stick your hand in ours and play with our flags! > > WTF is the workqueue code setting the PF_THREAD_BOUND flag manually? > Talk about fragile coupling! You just made this flag meaningless. Don't > do that. And looking at the hotplug code in that very file is just making me more nervous about that abuse. > Sorry but I just wasted two whole days because of this nonsense and I'm > not particularly happy about it. > > -- Steve > > Signed-off-by: Steven Rostedt > > > diff --git a/kernel/sched.c b/kernel/sched.c > index ec5f472..682a90c 100644 > --- a/kernel/sched.c > +++ b/kernel/sched.c > @@ -2233,6 +2233,9 @@ void set_task_cpu(struct task_struct *p, unsigned int new_cpu) > if (task_cpu(p) != new_cpu) { > p->se.nr_migrations++; > perf_sw_event(PERF_COUNT_SW_CPU_MIGRATIONS, 1, NULL, 0); > + if (WARN_ON(p->flags & PF_THREAD_BOUND)) > + printk(KERN_WARNING "migrating bounded task %s:%d\n", > + p->comm, p->pid); That should be a if (WARN(...)) and if triggers we should just refuse to migrate it. So probably set_task_cpu() is not the proper place for that. Can we move that check on layer up to avoid it reaching set_task_cpu() ? > } > > __set_task_cpu(p, new_cpu); And please submit a patch which gets rid of > worker->task->flags |= PF_THREAD_BOUND; Thanks, tglx