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=-15.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_SANE_1 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 6848FC6377D for ; Thu, 22 Jul 2021 08:47:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4A0B961351 for ; Thu, 22 Jul 2021 08:47:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231288AbhGVIHC (ORCPT ); Thu, 22 Jul 2021 04:07:02 -0400 Received: from foss.arm.com ([217.140.110.172]:47724 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230314AbhGVIHB (ORCPT ); Thu, 22 Jul 2021 04:07:01 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 91983113E; Thu, 22 Jul 2021 01:47:36 -0700 (PDT) Received: from [192.168.178.6] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D9B3D3F73D; Thu, 22 Jul 2021 01:47:34 -0700 (PDT) Subject: Re: [PATCH v4 2/2] sched: Skip priority checks with SCHED_FLAG_KEEP_PARAMS To: Quentin Perret , mingo@redhat.com, peterz@infradead.org, vincent.guittot@linaro.org, qais.yousef@arm.com, rickyiu@google.com, wvw@google.com, patrick.bellasi@matbug.net, xuewen.yan94@gmail.com Cc: linux-kernel@vger.kernel.org, kernel-team@android.com References: <20210719161656.3833943-1-qperret@google.com> <20210719161656.3833943-3-qperret@google.com> From: Dietmar Eggemann Message-ID: Date: Thu, 22 Jul 2021 10:47:33 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: <20210719161656.3833943-3-qperret@google.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/07/2021 18:16, Quentin Perret wrote: > SCHED_FLAG_KEEP_PARAMS can be passed to sched_setattr to specify that > the call must not touch scheduling parameters (nice or priority). This What about DL params (runtime, deadline, period)? Uclamp is not for DL but we could (*) still set uclamp values on a DL task. Obviously they would only be used when the task switches policy. On tip/sched/core: root@juno:~# chrt -d -P 1000000000 -T 100000000 -p 0 1671 root@juno:~# uclampset -m200 -M400 -p 1671 root@juno:~# cat /proc/1671/sched | grep uclamp uclamp.min : 200 uclamp.max : 400 effective uclamp.min : 200 effective uclamp.max : 400 root@juno:~# chrt -o -p 0 pid 1702's current scheduling policy: SCHED_OTHER pid 1702's current scheduling priority: 0 root@juno:~# cat /proc/1671/sched | grep uclamp uclamp.min : 200 uclamp.max : 400 effective uclamp.min : 200 effective uclamp.max : 400 > is particularly handy for uclamp when used in conjunction with > SCHED_FLAG_KEEP_POLICY as that allows to issue a syscall that only > impacts uclamp values. > > However, sched_setattr always checks whether the priorities and nice > values passed in sched_attr are valid first, even if those never get + DL params (__checkparam_dl()) > used down the line. This is useless at best since userspace can > trivially bypass this check to set the uclamp values by specifying low > priorities. However, it is cumbersome to do so as there is no single > expression of this that skips both RT and CFS checks at once. As such, > userspace needs to query the task policy first with e.g. sched_getattr > and then set sched_attr.sched_priority accordingly. This is racy and > slower than a single call. > > As the priority and nice checks are useless when SCHED_FLAG_KEEP_PARAMS > is specified, simply inherit them in this case to match the policy > inheritance of SCHED_FLAG_KEEP_POLICY. > > Reported-by: Wei Wang > Reviewed-by: Qais Yousef > Signed-off-by: Quentin Perret > --- > kernel/sched/core.c | 19 +++++++++++++------ > 1 file changed, 13 insertions(+), 6 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index e801d2c3077b..914076eab242 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -7332,6 +7332,16 @@ static int sched_copy_attr(struct sched_attr __user *uattr, struct sched_attr *a > return -E2BIG; > } > > +static void get_params(struct task_struct *p, struct sched_attr *attr) > +{ > + if (task_has_dl_policy(p)) > + __getparam_dl(p, attr); (*) This changes the behaviour when setting uclamp values on a DL task. Before uclamp values could be set but now, because of void __getparam_dl(struct task_struct *p, struct sched_attr *attr) .. attr->sched_flags = dl_se->flags SCHED_FLAG_UTIL_CLAMP gets overwritten and __sched_setscheduler() bails in: if (unlikely(policy == p->policy)) { ... retval = 0; goto unlock; } change: I.e. the: if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) goto change; can't trigger anymore. > + else if (task_has_rt_policy(p)) > + attr->sched_priority = p->rt_priority; > + else > + attr->sched_nice = task_nice(p); > +} > + > /** > * sys_sched_setscheduler - set/change the scheduler policy and RT priority > * @pid: the pid in question. > @@ -7393,6 +7403,8 @@ SYSCALL_DEFINE3(sched_setattr, pid_t, pid, struct sched_attr __user *, uattr, > rcu_read_unlock(); > > if (likely(p)) { > + if (attr.sched_flags & SCHED_FLAG_KEEP_PARAMS) > + get_params(p, &attr); SCHED_FLAG_KEEP_PARAMS is handled here but SCHED_FLAG_KEEP_POLICY outside (before) the `if (likely(p))`? > retval = sched_setattr(p, &attr); > put_task_struct(p); > } [...]