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=-4.0 required=3.0 tests=BAYES_00, 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 AFB20C433E1 for ; Thu, 13 Aug 2020 13:46:03 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 75B0520774 for ; Thu, 13 Aug 2020 13:46:03 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 75B0520774 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 158B28D0002; Thu, 13 Aug 2020 09:46:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 109BB6B0003; Thu, 13 Aug 2020 09:46:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id F39BB8D0002; Thu, 13 Aug 2020 09:46:02 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0101.hostedemail.com [216.40.44.101]) by kanga.kvack.org (Postfix) with ESMTP id DC41E6B0002 for ; Thu, 13 Aug 2020 09:46:02 -0400 (EDT) Received: from smtpin12.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 8599E824934B for ; Thu, 13 Aug 2020 13:46:02 +0000 (UTC) X-FDA: 77145668964.12.horn31_4c07f3e26ff4 Received: from filter.hostedemail.com (10.5.16.251.rfc1918.com [10.5.16.251]) by smtpin12.hostedemail.com (Postfix) with ESMTP id 41B281800A675 for ; Thu, 13 Aug 2020 13:46:02 +0000 (UTC) X-HE-Tag: horn31_4c07f3e26ff4 X-Filterd-Recvd-Size: 2575 Received: from mx2.suse.de (mx2.suse.de [195.135.220.15]) by imf39.hostedemail.com (Postfix) with ESMTP for ; Thu, 13 Aug 2020 13:46:01 +0000 (UTC) X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 27092B1B8; Thu, 13 Aug 2020 13:46:22 +0000 (UTC) Date: Thu, 13 Aug 2020 15:45:58 +0200 From: Michal Hocko To: Thomas Gleixner Cc: 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: <20200813134558.GM9477@dhcp22.suse.cz> References: <20200811210931.GZ4295@paulmck-ThinkPad-P72> <874kp87mca.fsf@nanos.tec.linutronix.de> <20200813075027.GD9477@dhcp22.suse.cz> <20200813095840.GA25268@pc636> <20200813111505.GG9477@dhcp22.suse.cz> <871rkallqk.fsf@nanos.tec.linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <871rkallqk.fsf@nanos.tec.linutronix.de> X-Rspamd-Queue-Id: 41B281800A675 X-Spamd-Result: default: False [0.00 / 100.00] X-Rspamd-Server: rspam01 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 Thu 13-08-20 15:27:15, Thomas Gleixner wrote: > Michal Hocko writes: > > On Thu 13-08-20 11:58:40, Uladzislau Rezki wrote: > > [...] > >> Sorry for jumping in. We can rely on preemptable() for sure, if CONFIG_PREEMPT_RT > >> is enabled, something like below: > >> > >> if (IS_ENABLED_RT && preemptebale()) > > > > Sure. I thought this was an RT specific thing that would be noop > > otherwise. > > Well, even if RT specific it would be still something returning either > true or false unconditionally. > > And guarding it with RT is not working either because then you are back > to square one with the problem which triggered the discussion in the > first place: > > raw_spin_lock() > alloc() > if (RT && !preemptible()) <- False because RT == false > goto bail; > > spin_lock(&zone->lock) --> LOCKDEP complains > > So either you convince Paul not to do that or you need to do something > like I suggested in my other reply. Can we somehow annotate the lock to be safe for nesting for lockdep? -- Michal Hocko SUSE Labs