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=-3.8 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,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 469A1C433DF for ; Thu, 13 Aug 2020 18:26:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 2A8E020829 for ; Thu, 13 Aug 2020 18:26:41 +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="VB2gdtur" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726570AbgHMS0j (ORCPT ); Thu, 13 Aug 2020 14:26:39 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50746 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726167AbgHMS0j (ORCPT ); Thu, 13 Aug 2020 14:26:39 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E4AE0C061757; Thu, 13 Aug 2020 11:26:38 -0700 (PDT) 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=g1eoHHh3zLR/ThuflE/IIEVilQA8iEgwq53pEaNkKwg=; b=VB2gdturL+7LgHaS8LxLHFXDTa bLTMvaJYqbwN4Db9n5mKZhleZEgHlz2IbIAi0Jc/dxJXlJLuKNbA2rhtlna4bMiUQnondbJF668XW MuheGCTTRBsEMYcm5O3a/PI4rEOP4VxowuFgfgerojrAcqDXntlo/4fVK+fBwTgC5RnjjjgQbTvcK 071pQthrqZnZEnFrOBHcmsWC52L+65BE5NqfomhXEFYC8y2Q9GVgxBb9NlJGu9bzH01JDRrdA3A4O ZBkDgPu/2VlwM+oRk75h9m3z0eWEMXlEx4l1zF3CJw0Ep15pvgq7cIDOgwUFOU09ItaBDn0Hhz20B /KqrI3lA==; 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 1k6Hvj-0001UJ-9N; Thu, 13 Aug 2020 18:26:23 +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 E2E823011F0; Thu, 13 Aug 2020 20:26:18 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id D632C2B3D4AD4; Thu, 13 Aug 2020 20:26:18 +0200 (CEST) Date: Thu, 13 Aug 2020 20:26:18 +0200 From: peterz@infradead.org To: Thomas Gleixner Cc: Michal Hocko , Uladzislau Rezki , paulmck@kernel.org, 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: <20200813182618.GX2674@hirez.programming.kicks-ass.net> References: <20200811210931.GZ4295@paulmck-ThinkPad-P72> <874kp87mca.fsf@nanos.tec.linutronix.de> <20200813075027.GD9477@dhcp22.suse.cz> <20200813095840.GA25268@pc636> <874kp6llzb.fsf@nanos.tec.linutronix.de> <20200813133308.GK9477@dhcp22.suse.cz> <87sgcqty0e.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87sgcqty0e.fsf@nanos.tec.linutronix.de> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Aug 13, 2020 at 04:34:57PM +0200, Thomas Gleixner wrote: > Michal Hocko writes: > > On Thu 13-08-20 15:22:00, Thomas Gleixner wrote: > >> It basically requires to convert the wait queue to something else. Is > >> the waitqueue strict single waiter? > > > > I would have to double check. From what I remember only kswapd should > > ever sleep on it. > > That would make it trivial as we could simply switch it over to rcu_wait. > > >> So that should be: > >> > >> if (!preemptible() && gfp == GFP_RT_NOWAIT) > >> > >> which is limiting the damage to those callers which hand in > >> GFP_RT_NOWAIT. > >> > >> lockdep will yell at invocations with gfp != GFP_RT_NOWAIT when it hits > >> zone->lock in the wrong context. And we want to know about that so we > >> can look at the caller and figure out how to solve it. > > > > Yes, that would have to somehow need to annotate the zone_lock to be ok > > in those paths so that lockdep doesn't complain. > > That opens the worst of all cans of worms. If we start this here then > Joe programmer and his dog will use these lockdep annotation to evade > warnings and when exposed to RT it will fall apart in pieces. Just that > at that point Joe programmer moved on to something else and the usual > suspects can mop up the pieces. We've seen that all over the place and > some people even disable lockdep temporarily because annotations don't > help. > > PeterZ might have opinions about that too I suspect. PeterZ is mightily confused by all of this -- also heat induced brain melt. I thought the rule was: - No allocators (alloc/free) inside raw_spinlock_t, full-stop. Why are we trying to craft an exception?