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 0F24FC04EB9 for ; Mon, 3 Dec 2018 08:39:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id CF82B2081C for ; Mon, 3 Dec 2018 08:39:48 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CF82B2081C 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 S1726105AbeLCIjt (ORCPT ); Mon, 3 Dec 2018 03:39:49 -0500 Received: from mx2.suse.de ([195.135.220.15]:52290 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725968AbeLCIjs (ORCPT ); Mon, 3 Dec 2018 03:39:48 -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 B5E14AEC6; Mon, 3 Dec 2018 08:39:44 +0000 (UTC) Date: Mon, 3 Dec 2018 09:39:42 +0100 From: Michal Hocko To: Ingo Molnar Cc: Linus Torvalds , Linux List Kernel Mailing , "Rafael J. Wysocki" , Chanho Min , Thomas Gleixner , Peter Zijlstra , Oleg Nesterov , Pavel Machek Subject: Re: [PATCH] Revert "exec: make de_thread() freezable (was: Re: Linux 4.20-rc4) Message-ID: <20181203083942.GF31738@dhcp22.suse.cz> References: <20181203074700.GA21240@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181203074700.GA21240@gmail.com> 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 Mon 03-12-18 08:47:00, Ingo Molnar wrote: [...] > I reviewed the ->cred_guard_mutex code, and the mutex is held across all > of exec() - and we always did this. Yes, this is something that has been pointed out during the review. Oleg has argued that making this path freezable is really hard and that we should be changing de_thread to sleep withtou cred_guard_mutex long term anyway (http://lkml.kernel.org/r/20181114143705.GB13885@redhat.com). Failing suspend seems like a real problem while the lockdep one doesn't really reflect any real deadlock, right? So while the patch is not perfect it shouldn't make the situation much worse. Lockdep splat is certainly annoying but is it any worse than a suspend failing? Now, I wouldn't mind to revert this because the code is really old and we haven't seen many bug reports about failing suspend yet. But what is the actual plan to make this work properly? Use freezable_schedule_unsafe instead? Freezer code has some fundamental design issues which are quite hard to get over. -- Michal Hocko SUSE Labs