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=HEADER_FROM_DIFFERENT_DOMAINS, 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 22A34C282D7 for ; Wed, 30 Jan 2019 16:52:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E0D4F2086C for ; Wed, 30 Jan 2019 16:52:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732296AbfA3QwG (ORCPT ); Wed, 30 Jan 2019 11:52:06 -0500 Received: from mx1.redhat.com ([209.132.183.28]:42029 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1732276AbfA3QwE (ORCPT ); Wed, 30 Jan 2019 11:52:04 -0500 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 1B3D4C0DA365; Wed, 30 Jan 2019 16:52:04 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.163]) by smtp.corp.redhat.com (Postfix) with SMTP id 9DA49176DE; Wed, 30 Jan 2019 16:52:02 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 30 Jan 2019 17:52:03 +0100 (CET) Date: Wed, 30 Jan 2019 17:52:01 +0100 From: Oleg Nesterov To: Roman Gushchin Cc: Tejun Heo , kernel-team@fb.com, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, Roman Gushchin Subject: Re: [PATCH v6 4/7] cgroup: cgroup v2 freezer Message-ID: <20190130165200.GA4131@redhat.com> References: <20181222000307.28231-1-guro@fb.com> <20181222000307.28231-5-guro@fb.com> <20190125122713.GA18218@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.31]); Wed, 30 Jan 2019 16:52:04 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Roman, On 01/28, Roman Gushchin wrote: > > Yes, I think you're right: cgroup_exit() should check CGRP_FREEZE bit, > not CGRP_FROZEN. Like cgroup_post_fork() does (a one-liner change below). but this won't fix all problems? it seems that you missed my other concerns. Firstly, this doesn't look consistent. Suppose a cgroup contains a single process sleeping in ptrace_stop(). Then it becomes CGRP_FROZEN right after "echo 1 > cgroup.freeze". OTOH. if this single task sleeps in do_freezer_trap() and gets PTRACE_INTERRUPT, it will equally sleep ptrace_stop() but cgroup won't be CGRP_FROZEN. Never. Worse, this looks just wrong. In the latter case, cgroup becomes CGRP_FROZEN right after a 2nd task migrates to this cgroup, before this new task calls do_freezer_trap() or cgroup_enter_stopped(). > About spurious transitions (like frozen->non frozen->frozen on a task > being SIGKILLed): > in early versions of the patchset I've tried to avoid them, but then > following the Tejun's advice > switched over to expose them to a user. The logic behind is simple: if > the state of the cgroup has been changed (a task is gone, for > example), let's notify a user. OK, I won't argue... actually I can't argue because I do not really understand why do we want a "killable" freezer, let alone ptraceable ;) Oleg.