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 90B9DC43381 for ; Mon, 25 Feb 2019 15:57:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 68E6520842 for ; Mon, 25 Feb 2019 15:57:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727772AbfBYP52 (ORCPT ); Mon, 25 Feb 2019 10:57:28 -0500 Received: from mx1.redhat.com ([209.132.183.28]:46130 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727505AbfBYP52 (ORCPT ); Mon, 25 Feb 2019 10:57:28 -0500 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4ACE5308624A; Mon, 25 Feb 2019 15:57:28 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id E7C6960863; Mon, 25 Feb 2019 15:57:26 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 25 Feb 2019 16:57:28 +0100 (CET) Date: Mon, 25 Feb 2019 16:57:25 +0100 From: Oleg Nesterov To: Tejun Heo Cc: Roman Gushchin , Roman Gushchin , Kernel Team , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v8 0/7] freezer for cgroup v2 Message-ID: <20190225155725.GA8096@redhat.com> References: <20190219220252.4906-1-guro@fb.com> <20190220143748.GA9477@redhat.com> <20190220220020.GA16335@castle.DHCP.thefacebook.com> <20190221162923.GA26064@redhat.com> <20190221173422.GY50184@devbig004.ftw2.facebook.com> <20190222163441.GA5596@redhat.com> <20190222181740.GZ50184@devbig004.ftw2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190222181740.GZ50184@devbig004.ftw2.facebook.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.49]); Mon, 25 Feb 2019 15:57:28 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/22, Tejun Heo wrote: > > > So I think it too should somehow interact with freezable_schedule/etc. > > You mean freezer_do_not_count(), right? yes, > As long as the task is > guaranteed to be trapped by signal stop afterwards (and they are), we > likely can use them the same way. The only thing to be careful about > would be ensuring that we don't end up flipping group level frozen > state inbetween. Would something like that work? I have no idea because I do not understand what exactly do you mean ;) However. Thinking more about this, I am not sure my concerns were valid. Yes, cg freezer can "hang" if it races with vfork(). But probably we should blame vfork(), not freezer. The problem is, even ^Z can "hang" if the foreground process does vfork() and the new child stops before exit/exec. Now I recall that I even tried to make a patch to fix this using ERESTART_RESTARTBLOCK, but had some nasty problems with blocked signals... de_thread() should use freezable_schedule() in TASK_KILLABLE too. Currently it doesn't, but only because we have other (much more serious) problems with cred_guard_mutex/exec. However, this is is fine wrt cg freezer, other threads can't be frozen exactly because it is killable. Anything else does freezer_do_not_count() in TASK_KILLABLE and waits for another freezable process? So it seems I have to take my words back, perhaps we can forget about freezable_schedule/etc. Oleg.