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 3039BC43441 for ; Wed, 14 Nov 2018 16:56:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 0145F208A3 for ; Wed, 14 Nov 2018 16:56:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0145F208A3 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com 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 S1732914AbeKODAd (ORCPT ); Wed, 14 Nov 2018 22:00:33 -0500 Received: from mx1.redhat.com ([209.132.183.28]:47418 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725828AbeKODAd (ORCPT ); Wed, 14 Nov 2018 22:00:33 -0500 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6E33E80462; Wed, 14 Nov 2018 16:56:34 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.31]) by smtp.corp.redhat.com (Postfix) with SMTP id 1B1D519744; Wed, 14 Nov 2018 16:56:32 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Wed, 14 Nov 2018 17:56:34 +0100 (CET) Date: Wed, 14 Nov 2018 17:56:32 +0100 From: Oleg Nesterov To: Roman Gushchin Cc: Roman Gushchin , Tejun Heo , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" , Kernel Team Subject: Re: [PATCH v2 3/6] cgroup: cgroup v2 freezer Message-ID: <20181114165631.GE13885@redhat.com> References: <20181112230422.5911-1-guro@fb.com> <20181112230422.5911-5-guro@fb.com> <20181113154825.GC30990@redhat.com> <20181113215919.GC15590@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181113215919.GC15590@tower.DHCP.thefacebook.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Wed, 14 Nov 2018 16:56:34 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Roman, On 11/13, Roman Gushchin wrote: > > > > +#define TASK_FROZEN 0x1000 > > > +#define TASK_STATE_MAX 0x2000 > > > > Just noticed the new task state... Why? Can't we avoid it? > > We can, but it's nice to show to userspace that tasks are frozen, > rather than just stuck somewhere in the kernel... But then you need to change get_task_state() too. Which iiuc could probably check ->frozen along with ->state. I do not think the new task state is a good idea, at least I would like to ask you to make a separate patch which we can discuss separately. > > > + set_current_state(TASK_WAKEKILL | TASK_INTERRUPTIBLE | TASK_FROZEN); > > > > Why not __set_current_state() ? > > Hm, it's not a hot path at all, so set_current_state() is good enough. > Not a strong preference, of course. It is not about performance, to me set_current_state() looks as if we need a memory barrier for some obscure/undocumented reason and this doesn't help to understand the code. > > If ->state include TASK_INTERRUPTIBLE, why do we need TASK_WAKEKILL? > > > > And again, why TASK_FROZEN? > > So, should it be just TASK_INTERRUPTIBLE | TASK_FROZEN ? Again, TASK_FROZEN is pointless at least until you change fs/proc or until you have wake_up_state(TASK_FROZEN). May be cgroup_do_freeze() and/or ptrace_attach() could use it, but see above, I'd suggest to make another patch. Looks like you need TASK_KILLABLE, see below. > > > + clear_thread_flag(TIF_SIGPENDING); > > > + schedule(); > > > + recalc_sigpending(); > > > > I simply can't understand these 3 lines above but I bet this is not correct ;) > > So, yeah, the problem is that if there is TIF_SIGPENDING bit set, schedule() > will return immediately, so we're getting pretty much a busy loop here. I suspected this answer ;) > This is a nasty workaround. No, this is very wrong. Just suppose the caller is killed right before clear_thread_flag(TIF_SIGPENDING). > I believe we can clear and not call recalc_sigpending() at all. Does this seem > to be correct? I think you need to simply remove both clear_thread_flag() and recalc_sigpending(). If schedule() is called in TASK_KILLABLE state it will return only if fatal_signal_pending() is true, and this is what we want, right? OK, it seems you are going to make the new version anyway, so I can wait for it and not read this series ;) Oleg.