Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754138AbbBFBbG (ORCPT ); Thu, 5 Feb 2015 20:31:06 -0500 Received: from szxga01-in.huawei.com ([119.145.14.64]:15320 "EHLO szxga01-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753747AbbBFBbD (ORCPT ); Thu, 5 Feb 2015 20:31:03 -0500 Message-ID: <54D4194B.2040808@huawei.com> Date: Fri, 6 Feb 2015 09:30:51 +0800 From: Zefan Li User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Peter Zijlstra CC: Ingo Molnar , Mike Galbraith , LKML , Stefan Bader Subject: Re: [PATCH] sched, autogroup: Fix failure when writing to cpu.rt_runtime_us References: <54D32AD4.1060003@huawei.com> <20150205142527.GI5029@twins.programming.kicks-ass.net> In-Reply-To: <20150205142527.GI5029@twins.programming.kicks-ass.net> X-Enigmail-Version: 1.6 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.18.230] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2423 Lines: 97 On 2015/2/5 22:25, Peter Zijlstra wrote: > On Thu, Feb 05, 2015 at 04:33:24PM +0800, Zefan Li wrote: >> This is how to reproduce the bug: >> >> int main() { >> struct sched_param param = {.sched_priority=1}; >> >> if (fork() > 0) >> exit(0); >> >> setsid(); >> >> if (sched_setscheduler(0, SCHED_RR, ¶m) < 0){ >> perror("failed to sched_setscheduler()"); >> return -1; >> } >> btw, if you move setscheduler() abvoe fork(), changing rt_runtime will succeed. >> while(1) >> ; >> } >> >> # ./test >> # mount -t cgroup -o cpu xxx /cgroup >> # cat /cgroup/cpu.rt_runtime_us >> 950000 >> # echo 940000 > /cgroup/cpu.rt_runtime_us >> Device or Resource busy > > That's -EBUSY, but you're changing an -EPERM condition. Neither your > patch nor explanation of the matter make sense. > I'm not changing the -EPERM condition. I'm adding an else condition which resets p->sched_task_group. After running the test program, we have: root | autogroup <-- the RT test program is now here root.rt_runtime = 950000 autogroup.rt_runtime = 0 Now if you try to change the rt_runtime of the root cgroup, it returns -EBUSY. That comes from: static int tg_rt_schedulable(struct task_group *tg, void *data) ( ... if (rt_bandwidth_enabled() && !runtime && tg_has_rt_tasks(tg)) return -EBUSY; ... } static inline int tg_has_rt_tasks(struct task_group *tg) { struct task_struct *g, *p; for_each_process_thread(g, p) { if (rt_task(p) && task_group(p) == tg) return 1; } return 0; } here tg == autogroup, p == the test program, and task_group(p) returns autogroup, which is wrong. See this commit: commit f44937718ce3b8360f72f6c68c9481712517a867 Author: Mike Galbraith Date: Thu Jan 13 04:54:50 2011 +0100 sched, autogroup: Fix CONFIG_RT_GROUP_SCHED sched_setscheduler() failure ... + /* + * Autogroup RT tasks are redirected to the root task group ... + * the policy change to proceed. Thereafter, task_group() + * returns &root_task_group, ... + */ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/