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 3F788C5519F for ; Wed, 25 Nov 2020 11:11:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A5B58206B5 for ; Wed, 25 Nov 2020 11:11:30 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="AJES3mm5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728544AbgKYLL3 (ORCPT ); Wed, 25 Nov 2020 06:11:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37350 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727827AbgKYLL3 (ORCPT ); Wed, 25 Nov 2020 06:11:29 -0500 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 046EBC0613D4 for ; Wed, 25 Nov 2020 03:11:29 -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=reKT6LG6AzTdzZ7PfWjq8eopMMV3Z6WkzXizdIvYzFk=; b=AJES3mm5nzzN9XS8gbjYNbrohe TNZKZtE3pgXCFSHA1ggdaccpY5IiGho20mYH8aUiMHrkox2ocVo9dRM2WaE7byR2+clSvOGQd87e7 UgaK7NuU5WLdmsngn/sZ4+SaN3n5NIbmG6wax+eyEy/hZ45/kULjqlUnXFMMntkDeyXnovcp4NfF6 5oAL01C+lI0p1K6TZS4QNAWRDiurQ+wVdk13FuG6aPpypMiHgmvKXdwXoSWVBFZrtTfnOXtRm3n6s 4fibQSYl/WjIQJLG7jJ2+PeDCVisikfHPHfTbnx8AgEmbMpl8BPXoRwhTip8IGPDrJuljVD7yr34a kciujeYw==; 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 1khsgi-00079r-N7; Wed, 25 Nov 2020 11:10:16 +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 8E36730280E; Wed, 25 Nov 2020 12:10:14 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 786B4200B84B2; Wed, 25 Nov 2020 12:10:14 +0100 (CET) Date: Wed, 25 Nov 2020 12:10:14 +0100 From: Peter Zijlstra To: "Joel Fernandes (Google)" 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: <20201125111014.GS2414@hirez.programming.kicks-ass.net> References: <20201117232003.3580179-1-joel@joelfernandes.org> <20201117232003.3580179-23-joel@joelfernandes.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201117232003.3580179-23-joel@joelfernandes.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 17, 2020 at 06:19:52PM -0500, Joel Fernandes (Google) wrote: > +void sched_core_tag_requeue(struct task_struct *p, unsigned long cookie, bool group) > +{ > + if (!p) > + return; > + > + if (group) > + p->core_group_cookie = cookie; > + else > + p->core_task_cookie = cookie; > + > + /* Use up half of the cookie's bits for task cookie and remaining for group cookie. */ > + p->core_cookie = (p->core_task_cookie << > + (sizeof(unsigned long) * 4)) + p->core_group_cookie; This seems dangerous; afaict there is nothing that prevents cookie collision.