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=-2.5 required=3.0 tests=MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT 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 705A4C4321D for ; Fri, 24 Aug 2018 13:32:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1AA4B2168B for ; Fri, 24 Aug 2018 13:32:15 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 1AA4B2168B Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727839AbeHXRGy (ORCPT ); Fri, 24 Aug 2018 13:06:54 -0400 Received: from mx2.suse.de ([195.135.220.15]:53586 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726969AbeHXRGy (ORCPT ); Fri, 24 Aug 2018 13:06:54 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 07764AF3C; Fri, 24 Aug 2018 13:32:10 +0000 (UTC) Date: Fri, 24 Aug 2018 15:32:07 +0200 From: Michal Hocko To: Tetsuo Handa Cc: =?iso-8859-1?B?Suly9G1l?= Glisse , Andrew Morton , LKML , linux-mm@kvack.org, "David (ChunMing) Zhou" , Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , Alex Deucher , David Airlie , Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Doug Ledford , Jason Gunthorpe , Mike Marciniszyn , Dennis Dalessandro , Sudeep Dutt , Ashutosh Dixit , Dimitri Sivanich , Boris Ostrovsky , Juergen Gross , Andrea Arcangeli , Felix Kuehling , kvm@vger.kernel.org, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-rdma@vger.kernel.org, xen-devel@lists.xenproject.org, Christian =?iso-8859-1?Q?K=F6nig?= , David Rientjes , Leon Romanovsky Subject: Re: [PATCH] mm, oom: distinguish blockable mode for mmu notifiers Message-ID: <20180824133207.GR29735@dhcp22.suse.cz> References: <20180716115058.5559-1-mhocko@kernel.org> <8cbfb09f-0c5a-8d43-1f5e-f3ff7612e289@I-love.SAKURA.ne.jp> <20180824113629.GI29735@dhcp22.suse.cz> <103b1b33-1a1d-27a1-dcf8-5c8ad60056a6@i-love.sakura.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <103b1b33-1a1d-27a1-dcf8-5c8ad60056a6@i-love.sakura.ne.jp> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 24-08-18 22:02:23, Tetsuo Handa wrote: > On 2018/08/24 20:36, Michal Hocko wrote: > >> That is, this API seems to be currently used by only out-of-tree users. Since > >> we can't check that nobody has memory allocation dependency, I think that > >> hmm_invalidate_range_start() should return -EAGAIN if blockable == false for now. > > > > The code expects that the invalidate_range_end doesn't block if > > invalidate_range_start hasn't blocked. That is the reason why the end > > callback doesn't have blockable parameter. If this doesn't hold then the > > whole scheme is just fragile because those two calls should pair. > > > That is > > More worrisome part in that patch is that I don't know whether using > trylock if blockable == false at entry is really sufficient. > > . Since those two calls should pair, I think that we need to determine whether > we need to return -EAGAIN at start call by evaluating both calls. Yes, and I believe I have done that audit. Module my misunderstanding of the code. > Like mn_invl_range_start() involves schedule_delayed_work() which could be > blocked on memory allocation under OOM situation, It doesn't because that code path is not invoked for the !blockable case. > I worry that (currently > out-of-tree) users of this API are involving work / recursion. I do not give a slightest about out-of-tree modules. They will have to accomodate to the new API. I have no problems to extend the documentation and be explicit about this expectation. diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h index 133ba78820ee..698e371aafe3 100644 --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -153,7 +153,9 @@ struct mmu_notifier_ops { * * If blockable argument is set to false then the callback cannot * sleep and has to return with -EAGAIN. 0 should be returned - * otherwise. + * otherwise. Please note that if invalidate_range_start approves + * a non-blocking behavior then the same applies to + * invalidate_range_end. * */ int (*invalidate_range_start)(struct mmu_notifier *mn, > And hmm_release() says that > > /* > * Drop mirrors_sem so callback can wait on any pending > * work that might itself trigger mmu_notifier callback > * and thus would deadlock with us. > */ > > and keeps "all operations protected by hmm->mirrors_sem held for write are > atomic". This suggests that "some operations protected by hmm->mirrors_sem held > for read will sleep (and in the worst case involves memory allocation > dependency)". Yes and so what? The clear expectation is that neither of the range notifiers do not sleep in !blocking mode. I really fail to see what you are trying to say. -- Michal Hocko SUSE Labs