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 9CB44C43441 for ; Fri, 23 Nov 2018 12:46:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5D91E20861 for ; Fri, 23 Nov 2018 12:46:47 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5D91E20861 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 S2394754AbeKWXat (ORCPT ); Fri, 23 Nov 2018 18:30:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:38460 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2390833AbeKWXat (ORCPT ); Fri, 23 Nov 2018 18:30:49 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 1F275AEC0; Fri, 23 Nov 2018 12:46:44 +0000 (UTC) Date: Fri, 23 Nov 2018 13:46:43 +0100 From: Michal Hocko To: Daniel Vetter Cc: Daniel Vetter , LKML , Linux MM , Intel Graphics Development , DRI Development , Andrew Morton , David Rientjes , Christian =?iso-8859-1?Q?K=F6nig?= , =?iso-8859-1?B?Suly9G1l?= Glisse , Daniel Vetter Subject: Re: [PATCH 2/3] mm, notifier: Catch sleeping/blocking for !blockable Message-ID: <20181123124643.GK8625@dhcp22.suse.cz> References: <20181122165106.18238-1-daniel.vetter@ffwll.ch> <20181122165106.18238-3-daniel.vetter@ffwll.ch> <20181123111237.GE8625@dhcp22.suse.cz> <20181123123838.GL4266@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181123123838.GL4266@phenom.ffwll.local> 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 23-11-18 13:38:38, Daniel Vetter wrote: > On Fri, Nov 23, 2018 at 12:12:37PM +0100, Michal Hocko wrote: > > On Thu 22-11-18 17:51:05, Daniel Vetter wrote: > > > We need to make sure implementations don't cheat and don't have a > > > possible schedule/blocking point deeply burried where review can't > > > catch it. > > > > > > I'm not sure whether this is the best way to make sure all the > > > might_sleep() callsites trigger, and it's a bit ugly in the code flow. > > > But it gets the job done. > > > > Yeah, it is quite ugly. Especially because it makes DEBUG config > > bahavior much different. So is this really worth it? Has this already > > discovered any existing bug? > > Given that we need an oom trigger to hit this we're not hitting this in CI > (oom is just way to unpredictable to even try). I'd kinda like to also add > some debug interface so I can provoke an oom kill of a specially prepared > process, to make sure we can reliably exercise this path without killing > the kernel accidentally. We do similar tricks for our shrinker already. Create a task with oom_score_adj = 1000 and trigger the oom killer via sysrq and you should get a predictable oom invocation and execution. [...] > Wrt the behavior difference: I guess we could put another counter into the > task struct, and change might_sleep() to check it. All under > CONFIG_DEBUG_ATOMIC_SLEEP only ofc. That would avoid the preempt-disable > sideeffect. My worry with that is that people will spot it, and abuse it > in creative ways that do affect semantics. See horrors like > drm_can_sleep() (and I'm sure gfx folks are not the only ones who > seriously lacked taste here). > > Up to the experts really how to best paint this shed I think. Actually I like a way to say non_block_{begin,end} and might_sleep firing inside that context. -- Michal Hocko SUSE Labs