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=-8.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 C4942C4708F for ; Wed, 2 Jun 2021 14:20:47 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 7629A610A1 for ; Wed, 2 Jun 2021 14:20:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7629A610A1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 03B078E003A; Wed, 2 Jun 2021 10:20:47 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id F2D928E0035; Wed, 2 Jun 2021 10:20:46 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DA6F38E003A; Wed, 2 Jun 2021 10:20:46 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0176.hostedemail.com [216.40.44.176]) by kanga.kvack.org (Postfix) with ESMTP id A80E68E0035 for ; Wed, 2 Jun 2021 10:20:46 -0400 (EDT) Received: from smtpin33.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 45FCABF1A for ; Wed, 2 Jun 2021 14:20:46 +0000 (UTC) X-FDA: 78208994892.33.74BEC66 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) by imf23.hostedemail.com (Postfix) with ESMTP id 85C87A00026B for ; Wed, 2 Jun 2021 14:20:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; 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=jwYPkOxp8bIiCCDES8Qxb1QGLyBu3SVZdBROZyNFfA0=; b=Xxv615xncdZQEFrr1bHRLMMu2U OqaCFWc54sHFbTJW13AtDPYewqZ8YcVTPwpd9Qc5OnoRpWsz8cfAQ9eSQ5KwoRC3/+EzjpcSDWh0H 7W8reQPpnsPRXAwnvQmGxgENdJISBUxRfQv5GPB1VAMjsjLbgKsStP7MzLEasOohCJxysGOkYECMg Gwxo27rOG3a3S55yEdquv7sYRJNKvPMn8Kfz+MsY9z6svoP1ekd/je9c+Jaqi8y/arGNfbGhikW+b mNh4hH1eic9Rqr3hoPm+9JiRu5HuJ/MAdfZebjLsT7iBJPHGKrZ9jTKO2FPHmhESyUiqFe2yraAZt seVktLsg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by desiato.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1loRjL-002ucj-FS; Wed, 02 Jun 2021 14:20:30 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 09CFB300269; Wed, 2 Jun 2021 16:20:29 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id EBF7120223DBF; Wed, 2 Jun 2021 16:20:28 +0200 (CEST) Date: Wed, 2 Jun 2021 16:20:28 +0200 From: Peter Zijlstra To: Mathieu Desnoyers Cc: Thomas Gleixner , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , rostedt , Ben Segall , Mel Gorman , bristot , Borislav Petkov , x86 , "H. Peter Anvin" , Jens Axboe , Alasdair Kergon , Mike Snitzer , dm-devel , "David S. Miller" , Jakub Kicinski , Felipe Balbi , Greg Kroah-Hartman , Alexander Viro , Tejun Heo , Zefan Li , Johannes Weiner , Jason Wessel , Daniel Thompson , Douglas Anderson , acme , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , "Rafael J. Wysocki" , Pavel Machek , Will Deacon , Waiman Long , Boqun Feng , Oleg Nesterov , Davidlohr Bueso , paulmck , Josh Triplett , Lai Jiangshan , "Joel Fernandes, Google" , John Stultz , Stephen Boyd , Andrew Morton , Paolo Bonzini , linux-kernel , linux-block , netdev , linux-usb , linux-fsdevel , cgroups , kgdb-bugreport , linux-perf-users , linux-pm , rcu , linux-mm , KVM list Subject: Re: [PATCH 6/6] sched: Change task_struct::state Message-ID: References: <20210602131225.336600299@infradead.org> <20210602133040.587042016@infradead.org> <896642516.5866.1622642818225.JavaMail.zimbra@efficios.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <896642516.5866.1622642818225.JavaMail.zimbra@efficios.com> X-Rspamd-Queue-Id: 85C87A00026B Authentication-Results: imf23.hostedemail.com; dkim=pass header.d=infradead.org header.s=desiato.20200630 header.b=Xxv615xn; spf=none (imf23.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.92.199) smtp.mailfrom=peterz@infradead.org; dmarc=none X-Rspamd-Server: rspam04 X-Stat-Signature: ax1r15ahujcajkgtiro6xppc7fr6om9a X-HE-Tag: 1622643634-629676 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Jun 02, 2021 at 10:06:58AM -0400, Mathieu Desnoyers wrote: > ----- On Jun 2, 2021, at 9:12 AM, Peter Zijlstra peterz@infradead.org wrote: > > @@ -134,14 +134,14 @@ struct task_group; > > do { \ > > WARN_ON_ONCE(is_special_task_state(state_value));\ > > current->task_state_change = _THIS_IP_; \ > > - current->state = (state_value); \ > > + WRITE_ONCE(current->__state, (state_value)); \ > > } while (0) > > Why not introduce set_task_state(p) and get_task_state(p) rather than sprinkle > READ_ONCE() and WRITE_ONCE() all over the kernel ? set_task_state() is fundamentally unsound, there's very few sites that _set_ state on anything other than current, and those sites are super tricky, eg. ptrace. Having get_task_state() would seem to suggest it's actually a sane thing to do, it's not really. Inspecting remote state is full of races, and some of that really wants cleaning up, but that's for another day.