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=-5.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,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 59A38C0650F for ; Mon, 5 Aug 2019 11:53:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E1DB206A2 for ; Mon, 5 Aug 2019 11:53:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="2lc6U5MS" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728664AbfHELxf (ORCPT ); Mon, 5 Aug 2019 07:53:35 -0400 Received: from merlin.infradead.org ([205.233.59.134]:48786 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727739AbfHELxe (ORCPT ); Mon, 5 Aug 2019 07:53:34 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=Msf2V2we4WXS20WMdFiMZ4D3iFIy0buao6uIC50MNEM=; b=2lc6U5MS0+V8U+XyrODAUQr8/ CdcuDfc2HJzLfIrLWjo1cHIU13z7jI9RX+srG3MSgbBjXJ1XBXkGfYZA3cfB41HHdKAtQdmWcUrBx F+x6T/5e/Hw7kDXXZGPrJG1sbTTwshMUCXSC5zoK9OELCuEoXMOf1qWXMCajr7W9Y0/woknw5xiAj LQwN+BctbI7HgdPHspw0Ng45+wctKf4ncjlT5f01HpWqhVi5DCf8wL77mzgiO0ZlbZGaBFfQZ380o f0rs92irlijFE2DoF4JK3wu7qSA7wKLXjCr+V1HdvgOZrJgzIUbDEgh0WSYZDW12ItYuNSP9FLMx5 2FMLXc5Kw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92 #3 (Red Hat Linux)) id 1hubY7-0007xS-3r; Mon, 05 Aug 2019 11:53:11 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 38BB82022940D; Mon, 5 Aug 2019 13:53:09 +0200 (CEST) Date: Mon, 5 Aug 2019 13:53:09 +0200 From: Peter Zijlstra To: Alessio Balsini Cc: mingo@kernel.org, juri.lelli@redhat.com, linux-kernel@vger.kernel.org, dietmar.eggemann@arm.com, luca.abeni@santannapisa.it, bristot@redhat.com, dvyukov@google.com, tglx@linutronix.de, vpillai@digitalocean.com, rostedt@goodmis.org Subject: Re: [RFC][PATCH 01/13] sched/deadline: Impose global limits on sched_attr::sched_period Message-ID: <20190805115309.GJ2349@hirez.programming.kicks-ass.net> References: <20190726145409.947503076@infradead.org> <20190726161357.397880775@infradead.org> <20190802172104.GA134279@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190802172104.GA134279@google.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Aug 02, 2019 at 06:21:04PM +0100, Alessio Balsini wrote: > Hi Peter, > > This is indeed an important missing piece. > > I think it would be worth having some simple checks, e.g.: > - period_min <= period_max; > - period_min >= (1ULL << DL_SCALE). > > To be even more picky, I'm wondering if it would be a good practice to > fail the write operation if there are already dl-tasks in the system > that violate the new constraint. I'm afraid there is no cheap way of > achieving such check, so, I think we can skip this last tricky thing for > now. Like so? --- Subject: sched/deadline: Impose global limits on sched_attr::sched_period From: Peter Zijlstra Date: Tue Jul 23 16:01:29 CEST 2019 There are two DoS scenarios with SCHED_DEADLINE related to sched_attr::sched_period: - since access-control only looks at utilization and density, a very large period can allow a very large runtime, which in turn can incur a very large latency to lower priority tasks. - for very short periods we can end up spending more time programming the hardware timer than actually running the task. Mitigate these by imposing limits on the period. Signed-off-by: Peter Zijlstra (Intel) Cc: Daniel Bristot de Oliveira Cc: Luca Abeni Cc: Juri Lelli Cc: Dmitry Vyukov --- include/linux/sched/sysctl.h | 7 ++++ kernel/sched/deadline.c | 61 +++++++++++++++++++++++++++++++++++++++++-- kernel/sysctl.c | 14 +++++++++ 3 files changed, 80 insertions(+), 2 deletions(-) --- a/include/linux/sched/sysctl.h +++ b/include/linux/sched/sysctl.h @@ -56,6 +56,13 @@ int sched_proc_update_handler(struct ctl extern unsigned int sysctl_sched_rt_period; extern int sysctl_sched_rt_runtime; +extern unsigned int sysctl_sched_dl_period_max; +extern unsigned int sysctl_sched_dl_period_min; + +extern int sched_dl_period_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos); + #ifdef CONFIG_UCLAMP_TASK extern unsigned int sysctl_sched_uclamp_util_min; extern unsigned int sysctl_sched_uclamp_util_max; --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -2660,6 +2660,52 @@ void __getparam_dl(struct task_struct *p } /* + * Default limits for DL period; on the top end we guard against small util + * tasks still getting ridiculous long effective runtimes, on the bottom end we + * guard against timer DoS. + */ +unsigned int sysctl_sched_dl_period_max = 1 << 22; /* ~4 seconds */ +unsigned int sysctl_sched_dl_period_min = 100; /* 100 us */ + +int sched_dl_period_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, + loff_t *ppos) +{ + unsigned int old_min, old_max; + static DEFINE_MUTEX(mutex); + int ret; + + mutex_lock(&mutex); + old_min = sysctl_sched_dl_period_min; + old_max = sysctl_sched_dl_period_max; + + ret = proc_dointvec(table, write, buffer, lenp, ppos); + + if (!ret && write) { + u64 min = (u64)sysctl_sched_dl_period_min * NSEC_PER_USEC; + u64 max = (u64)sysctl_sched_dl_period_man * NSEC_PER_USEC; + + ret = -EINVAL; + if (min < 1ULL << DL_SCALE) + goto undo; + + if (max < min) + goto undo; + + ret = 0; + } + + if (0) { +undo: + sysctl_sched_rt_period = old_period; + sysctl_sched_rt_runtime = old_runtime; + } + mutex_unlock(&mutex); + + return ret; +} + +/* * This function validates the new parameters of a -deadline task. * We ask for the deadline not being zero, and greater or equal * than the runtime, as well as the period of being zero or @@ -2671,6 +2717,8 @@ void __getparam_dl(struct task_struct *p */ bool __checkparam_dl(const struct sched_attr *attr) { + u64 period, max, min; + /* special dl tasks don't actually use any parameter */ if (attr->sched_flags & SCHED_FLAG_SUGOV) return true; @@ -2694,12 +2742,21 @@ bool __checkparam_dl(const struct sched_ attr->sched_period & (1ULL << 63)) return false; + period = attr->sched_period; + if (!period) + period = attr->sched_deadline; + /* runtime <= deadline <= period (if period != 0) */ - if ((attr->sched_period != 0 && - attr->sched_period < attr->sched_deadline) || + if (period < attr->sched_deadline || attr->sched_deadline < attr->sched_runtime) return false; + max = (u64)READ_ONCE(sysctl_sched_dl_period_max) * NSEC_PER_USEC; + min = (u64)READ_ONCE(sysctl_sched_dl_period_min) * NSEC_PER_USEC; + + if (period < min || period > max) + return false; + return true; } --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -443,6 +443,20 @@ static struct ctl_table kern_table[] = { .proc_handler = sched_rt_handler, }, { + .procname = "sched_deadline_period_max_us", + .data = &sysctl_sched_dl_period_max, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = sched_dl_period_handler, + }, + { + .procname = "sched_deadline_period_min_us", + .data = &sysctl_sched_dl_period_min, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = sched_dl_period_handler, + }, + { .procname = "sched_rr_timeslice_ms", .data = &sysctl_sched_rr_timeslice, .maxlen = sizeof(int),