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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 7CF5CC433F5 for ; Thu, 6 Sep 2018 17:21:58 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3160A2075B for ; Thu, 6 Sep 2018 17:21:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3160A2075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728952AbeIFV6X (ORCPT ); Thu, 6 Sep 2018 17:58:23 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:48978 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727705AbeIFV6W (ORCPT ); Thu, 6 Sep 2018 17:58:22 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id CEF307A9; Thu, 6 Sep 2018 10:21:53 -0700 (PDT) Received: from e110439-lin (e110439-lin.emea.arm.com [10.4.12.126]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0C6D13F557; Thu, 6 Sep 2018 10:21:50 -0700 (PDT) Date: Thu, 6 Sep 2018 18:21:45 +0100 From: Patrick Bellasi To: Juri Lelli Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, Ingo Molnar , Peter Zijlstra , Tejun Heo , "Rafael J . Wysocki" , Viresh Kumar , Vincent Guittot , Paul Turner , Quentin Perret , Dietmar Eggemann , Morten Rasmussen , Todd Kjos , Joel Fernandes , Steve Muckle , Suren Baghdasaryan Subject: Re: [PATCH v4 14/16] sched/core: uclamp: request CAP_SYS_ADMIN by default Message-ID: <20180906172145.GA20623@e110439-lin> References: <20180828135324.21976-1-patrick.bellasi@arm.com> <20180828135324.21976-15-patrick.bellasi@arm.com> <20180904134748.GA4974@localhost.localdomain> <20180906144053.GD25636@e110439-lin> <20180906145936.GF27626@localhost.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180906145936.GF27626@localhost.localdomain> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06-Sep 16:59, Juri Lelli wrote: > On 06/09/18 15:40, Patrick Bellasi wrote: > > On 04-Sep 15:47, Juri Lelli wrote: > > [...] > > > > Wondering if you want to fold the check below inside the > > > > > > if (user && !capable(CAP_SYS_NICE)) { > > > ... > > > } > > > > > > block. It would also save you from adding another parameter to the > > > function. > > > > So, there are two reasons for that: > > > > 1) _I think_ we don't want to depend on capable(CAP_SYS_NICE) but > > instead on capable(CAP_SYS_ADMIN) > > > > Does that make sense ? > > > > If yes, the I cannot fold it in the block you reported above > > because we will not check for users with CAP_SYS_NICE. > > Ah, right, not sure though. Looks like CAP_SYS_NICE is used for settings > that relates to priorities, affinity, etc.: CPU related stuff. Since > here you are also dealing with something that seems to fall into the > same realm, it might actually fit more than CAP_SYS_ADMIN? Yes and no... from the functional standpoint if a task is running in the root cgroup, or cgroups are not in use at all, with this API a task can always ask for the max OPP. Which is what CAP_SYS_NICE is there for AFAIU... but... ... this check was meant also to fix the issue of the limited number of clamp groups. That's why I'm now asking for CAP_SYS_ADMIN. However, I would say that if we condsider to get in also the discretization support introduced in: [PATCH v4 15/16] sched/core: uclamp: add clamp group discretization support https://lore.kernel.org/lkml/20180828135324.21976-16-patrick.bellasi@arm.com/ then yes, we remain with the "nice" semantics to cover, and CAP_SYS_NICE could be just enough. > Now that I think more about it, would it actually make sense to allow > unpriviledged users to lower their assigned umin/umax properties if they > want? Something alike what happens for nice values or RT priorities. Yes... if we fix the issue with the limited clamp groups, i.e. we take discretization in. > > 2) Then we could move it after that block, where there is another > > set of checks with just: > > > > if (user) { > > > > We can potentially add the check there yes... but when uclamp is > > not enabled we will still perform those checks or we have to add > > some compiler guards... > > > > 3) ... or at least check for: > > > > if (attr->sched_flags & SCHED_FLAG_UTIL_CLAMP) > > > > Which is what I'm doing right after the block above (2). > > > > But, at this point, by passing in the parameter to the > > __setscheduler_uclamp() call, I get the benefits of: > > > > a) reducing uclamp specific code in the caller > > b) avoiding the checks on !CONFIG_UCLAMP_TASK build > > > > > > { > > > > int group_id[UCLAMP_CNT] = { UCLAMP_NOT_VALID }; > > > > int lower_bound, upper_bound; > > > > struct uclamp_se *uc_se; > > > > int result = 0; > > > > > > > > + if (!capable(CAP_SYS_ADMIN) && > > > > + user && !uclamp_user_allowed) { > > > > + return -EPERM; > > > > + } > > > > + > > > > Does all the above makes sense ? > > If we agree on CAP_SYS_ADMIN, however, your approach looks cleaner yes. Cheers Patrick -- #include Patrick Bellasi