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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 1D6ADC8300F for ; Tue, 1 Dec 2020 19:22:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 83AB4217A0 for ; Tue, 1 Dec 2020 19:22:45 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Zi0+mLPZ" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731317AbgLATWf (ORCPT ); Tue, 1 Dec 2020 14:22:35 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35204 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727431AbgLATWe (ORCPT ); Tue, 1 Dec 2020 14:22:34 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F983C0613CF for ; Tue, 1 Dec 2020 11:21:54 -0800 (PST) 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; bh=7JLyHZJtRdTTbCdr1AWpBIMP6N5KB46ClouAigDfKUM=; b=Zi0+mLPZRtmx6Nr/4ObCeXRnwl y1bv6dKyo7ObW5HiWKUIfQpK2UtTP5vww1zNY9ah095pZZKchDqdjtYIM4HBu8NJL9qfTzORE+xDm VKevGhyLJSwikXmpSornfpNjZ0RBKgxefODTrOK9TrnzV3vw9OeBeGojrCUIgTH+/xzfZ8n+2tlLX t14IVJfgnR/9U9EQET1LknHKYts+BdgJGUfSDd6dNprynsEmcuGppBhYiyyd4xn1RPiZTe2RR7fGa Z9RZanDBctLqnyBsXpqNarcEUYqXhsjf42lmDYBa2xWtl50U3/Fxoa74ZFSh+s6iXi5/tO87RDb34 T3Y2YGcA==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkBCn-0003j8-V0; Tue, 01 Dec 2020 19:20:54 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 4ED29305C22; Tue, 1 Dec 2020 20:20:50 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 39A4C2BF19AAE; Tue, 1 Dec 2020 20:20:50 +0100 (CET) Date: Tue, 1 Dec 2020 20:20:50 +0100 From: Peter Zijlstra To: Joel Fernandes Cc: Nishanth Aravamudan , Julien Desfossez , Tim Chen , Vineeth Pillai , Aaron Lu , Aubrey Li , tglx@linutronix.de, linux-kernel@vger.kernel.org, mingo@kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, keescook@chromium.org, kerrnel@google.com, Phil Auld , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini , vineeth@bitbyteword.org, Chen Yu , Christian Brauner , Agata Gruza , Antonio Gomez Iglesias , graf@amazon.com, konrad.wilk@oracle.com, dfaggioli@suse.com, pjt@google.com, rostedt@goodmis.org, derkling@google.com, benbjiang@tencent.com, Alexandre Chartre , James.Bottomley@hansenpartnership.com, OWeisse@umich.edu, Dhaval Giani , Junaid Shahid , jsbarnes@google.com, chris.hyser@oracle.com, Ben Segall , Josh Don , Hao Luo , Tom Lendacky , Aubrey Li , "Paul E. McKenney" , Tim Chen Subject: Re: [PATCH -tip 22/32] sched: Split the cookie and setup per-task cookie on fork Message-ID: <20201201192050.GX3040@hirez.programming.kicks-ass.net> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-23-joel@joelfernandes.org> <20201125111541.GU2414@hirez.programming.kicks-ass.net> <20201201191133.GA221478@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201201191133.GA221478@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 01, 2020 at 02:11:33PM -0500, Joel Fernandes wrote: > On Wed, Nov 25, 2020 at 12:15:41PM +0100, Peter Zijlstra wrote: > > On Tue, Nov 17, 2020 at 06:19:52PM -0500, Joel Fernandes (Google) wrote: > > > > > +/* > > > + * Ensure that the task has been requeued. The stopper ensures that the task cannot > > > + * be migrated to a different CPU while its core scheduler queue state is being updated. > > > + * It also makes sure to requeue a task if it was running actively on another CPU. > > > + */ > > > +static int sched_core_task_join_stopper(void *data) > > > +{ > > > + struct sched_core_task_write_tag *tag = (struct sched_core_task_write_tag *)data; > > > + int i; > > > + > > > + for (i = 0; i < 2; i++) > > > + sched_core_tag_requeue(tag->tasks[i], tag->cookies[i], false /* !group */); > > > + > > > + return 0; > > > +} > > > + > > > +static int sched_core_share_tasks(struct task_struct *t1, struct task_struct *t2) > > > +{ > > > > > + stop_machine(sched_core_task_join_stopper, (void *)&wr, NULL); > > > > > +} > > > > This is *REALLY* terrible... > > I pulled this bit from your original patch. Are you concerned about the > stop_machine? Sharing a core is a slow path for our usecases (and as far as I > know, for everyone else's). We can probably do something different if that > requirement changes. > Yeah.. so I can (and was planning on) remove stop_machine() from sched_core_{dis,en}able() before merging it. (there's two options, one uses stop_cpus() with the SMT mask, the other RCU) This though is exposing stop_machine() to joe user. Everybody is allowed to prctl() it's own task and set a cookie on himself. This means you just made giant unpriv DoS vector. stop_machine is bad, really bad.