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=-5.6 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 108B1C433DF for ; Fri, 14 Aug 2020 20:41:42 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CF6B220771 for ; Fri, 14 Aug 2020 20:41:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597437701; bh=scyrwTbuHhuKlqtV11BJGT5nyPFK8M5OUoE49z9q3L0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=MC7hUL1SP9KosB8cCsg2xSFj3qwDDgOHgcui0tWGjxuhd7JesFz+UFR1Plbyzdil6 z9DJVzA7sI1zU6cDGcs55JoZoEZmjrbyIdoeBTMxXp4TE7og21XRxH8IqntI0oRuJA Ds4HTJRPrAAeM9OE9HMEvTfBiYF+2fQtb5Yu/+Lw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726623AbgHNUll (ORCPT ); Fri, 14 Aug 2020 16:41:41 -0400 Received: from mail.kernel.org ([198.145.29.99]:55688 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726229AbgHNUll (ORCPT ); Fri, 14 Aug 2020 16:41:41 -0400 Received: from paulmck-ThinkPad-P72.home (unknown [50.45.173.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id D32C7206C0; Fri, 14 Aug 2020 20:41:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1597437700; bh=scyrwTbuHhuKlqtV11BJGT5nyPFK8M5OUoE49z9q3L0=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=VlDm3ljGDrUfdey3ROSk1O1NkkMzrkQ8jJLPNB5pyJkVI2ukM2igYZ7D63kWNXjt9 vfIVkU6ciD2PWaWe0MjY/V5yQwXs1Iya07GwhVhYKk+FU4LKMnma6/IErBkkyeVYlu 7VLKyFFoNhbGclMUXS1oiGdnO+vLz3mz1jgz4e1A= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id AE20E3522A0E; Fri, 14 Aug 2020 13:41:40 -0700 (PDT) Date: Fri, 14 Aug 2020 13:41:40 -0700 From: "Paul E. McKenney" To: Thomas Gleixner Cc: Peter Zijlstra , Michal Hocko , Uladzislau Rezki , LKML , RCU , linux-mm@kvack.org, Andrew Morton , Vlastimil Babka , Matthew Wilcox , "Theodore Y . Ts'o" , Joel Fernandes , Sebastian Andrzej Siewior , Oleksiy Avramchenko Subject: Re: [RFC-PATCH 1/2] mm: Add __GFP_NO_LOCKS flag Message-ID: <20200814204140.GT4295@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200813182618.GX2674@hirez.programming.kicks-ass.net> <20200813185257.GF4295@paulmck-ThinkPad-P72> <20200813220619.GA2674@hirez.programming.kicks-ass.net> <875z9m3xo7.fsf@nanos.tec.linutronix.de> <20200814083037.GD3982@worktop.programming.kicks-ass.net> <20200814141425.GM4295@paulmck-ThinkPad-P72> <20200814161106.GA13853@paulmck-ThinkPad-P72> <20200814174924.GI3982@worktop.programming.kicks-ass.net> <20200814180224.GQ4295@paulmck-ThinkPad-P72> <875z9lkoo4.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <875z9lkoo4.fsf@nanos.tec.linutronix.de> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Fri, Aug 14, 2020 at 09:33:47PM +0200, Thomas Gleixner wrote: > On Fri, Aug 14 2020 at 11:02, Paul E. McKenney wrote: > > On Fri, Aug 14, 2020 at 07:49:24PM +0200, Peter Zijlstra wrote: > >> On Fri, Aug 14, 2020 at 09:11:06AM -0700, Paul E. McKenney wrote: > >> > Just to make sure we are talking about the same thing, please see below > >> > for an untested patch that illustrates how I was interpreting your words. > >> > Was this what you had in mind? > >> > >> No, definitely not. > >> > >> Also, since we used to be able to use call_rcu() _everywhere_, including > >> under zone->lock, how's that working with you calling the > >> page-allocating from it? > > > > Indeed, that is exactly the problem we are trying to solve. > > Wait a moment. Why are we discussing RT induced raw non raw lock > ordering at all? Because we like to argue? (Sorry, couldn't resist.) > Whatever kernel you variant you look at this is not working: > > lock(zone) call_rcu() lock(zone) > > It's a simple recursive dead lock, nothing else. You are of course absolutely correct. > And that enforces the GFP_NOLOCK allocation mode or some other solution > unless you make a new rule that calling call_rcu() is forbidden while > holding zone lock or any other lock which might be nested inside the > GFP_NOWAIT zone::lock held region. Again, you are correct. Maybe the forecasted weekend heat will cause my brain to hallucinate a better solution, but in the meantime, the GFP_NOLOCK approach looks good from this end. Thanx, Paul