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 39F53C282DF for ; Fri, 19 Apr 2019 18:51:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1272B20663 for ; Fri, 19 Apr 2019 18:51:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728405AbfDSSvU (ORCPT ); Fri, 19 Apr 2019 14:51:20 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33962 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725882AbfDSSvT (ORCPT ); Fri, 19 Apr 2019 14:51:19 -0400 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E803ACD4A8; Fri, 19 Apr 2019 16:26:02 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.38]) by smtp.corp.redhat.com (Postfix) with SMTP id 994D71001E98; Fri, 19 Apr 2019 16:26:01 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Fri, 19 Apr 2019 18:26:02 +0200 (CEST) Date: Fri, 19 Apr 2019 18:26:00 +0200 From: Oleg Nesterov To: Roman Gushchin Cc: Roman Gushchin , Tejun Heo , Kernel Team , "cgroups@vger.kernel.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v10 4/9] cgroup: cgroup v2 freezer Message-ID: <20190419162600.GC12228@redhat.com> References: <20190405174708.1010-1-guro@fb.com> <20190405174708.1010-5-guro@fb.com> <20190419151912.GA12152@redhat.com> <20190419161118.GA23357@tower.DHCP.thefacebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190419161118.GA23357@tower.DHCP.thefacebook.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 19 Apr 2019 16:26:03 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/19, Roman Gushchin wrote: > > > Once again, suppose we race with CGRP_FREEZE. If JOBCTL_TRAP_FREEZE is already > > set then signal_pending() must be already T and we do not need recalc_sigpending? > > If JOBCTL_TRAP_FREEZE is not set yet, how can recalc_sigpending() help? > > This is paired with cgroup_task_frozen() check in recalc_sigpending_tsk(). Ooh, I didn't notice this version added cgroup_task_frozen() into recalc_sigpending_tsk() ... Honestly, I don't like this. But see another email I sent, we can cleanup this code later. > > > +static void cgroup_freeze_task(struct task_struct *task, bool freeze) > > > +{ > > > + unsigned long flags; > > > + > > > + /* If the task is about to die, don't bother with freezing it. */ > > > + if (!lock_task_sighand(task, &flags)) > > > + return; > > > + > > > + if (freeze) { > > > + task->jobctl |= JOBCTL_TRAP_FREEZE; > > > + signal_wake_up(task, false); > > > + } else { > > > + task->jobctl &= ~JOBCTL_TRAP_FREEZE; > > > + wake_up_process(task); > > > > wake_up_interruptible() ? > > Wait_up_interruptible() is supposed to work with a workqueue, > but here there is nothing like this. Probably, I didn't understand your idea. > Can you, please, elaborate a bit more? Not sure I understand... We need to wake up the task if it sleeps in do_freezer_trap(), right? do_freezer_trap() uses TASK_INTERRUPTIBLE, so why can't wake_up_interruptible() == __wake_up(TASK_INTERRUPTIBLE) work? > > > static int ptrace_signal(int signr, kernel_siginfo_t *info) > > > { > > > /* > > > @@ -2442,6 +2483,10 @@ bool get_signal(struct ksignal *ksig) > > > ksig->info.si_signo = signr = SIGKILL; > > > sigdelset(¤t->pending.signal, SIGKILL); > > > recalc_sigpending(); > > > + current->jobctl &= ~JOBCTL_TRAP_FREEZE; > > > + spin_unlock_irq(&sighand->siglock); > > > + if (unlikely(cgroup_task_frozen(current))) > > > + cgroup_leave_frozen(true); > > > > Oh, and another leave_frozen below... > > Yeah, because of this new "goto fatal" shortcut. I understand, but the code doesn't look nice... but again, I can't suggest anything better at least right now, so please forget. > > > + if (unlikely(cgroup_task_frozen(current))) { > > > spin_unlock_irq(&sighand->siglock); > > > + cgroup_leave_frozen(true); > > > goto relock; > > > } > > > > afaics cgroup_leave_frozen(false) makes more sense here. > > Why? I don't see any reasons why the task should remain in the frozen > state after this point. But cgroup_leave_frozen(false) will equally clear ->frozen if !CGRP_FREEZE ? OTOH, if CGRP_FREEZE is set again, why do we need to clear ->frozen? Oleg.