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=-2.3 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 29421C04AA5 for ; Mon, 15 Oct 2018 12:05:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E6C442064A for ; Mon, 15 Oct 2018 12:05:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org E6C442064A 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 S1726627AbeJOTud (ORCPT ); Mon, 15 Oct 2018 15:50:33 -0400 Received: from mx1.redhat.com ([209.132.183.28]:33992 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726319AbeJOTud (ORCPT ); Mon, 15 Oct 2018 15:50:33 -0400 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 B1A35CF21; Mon, 15 Oct 2018 12:05:32 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.106]) by smtp.corp.redhat.com (Postfix) with SMTP id 9E24B45A5; Mon, 15 Oct 2018 12:05:22 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Mon, 15 Oct 2018 14:05:32 +0200 (CEST) Date: Mon, 15 Oct 2018 14:05:21 +0200 From: Oleg Nesterov To: Enke Chen Cc: Thomas Gleixner , Ingo Molnar , Borislav Petkov , "H. Peter Anvin" , x86@kernel.org, Peter Zijlstra , Arnd Bergmann , "Eric W. Biederman" , Khalid Aziz , Kate Stewart , Helge Deller , Greg Kroah-Hartman , Al Viro , Andrew Morton , Christian Brauner , Catalin Marinas , Will Deacon , Dave Martin , Mauro Carvalho Chehab , Michal Hocko , Rik van Riel , "Kirill A. Shutemov" , Roman Gushchin , Marcos Paulo de Souza , Dominik Brodowski , Cyrill Gorcunov , Yang Shi , Jann Horn , Kees Cook , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, "Victor Kamensky (kamensky)" , xe-linux-external@cisco.com, Stefan Strogin , Eugene Syromiatnikov Subject: Re: [PATCH] kernel/signal: Signal-based pre-coredump notification Message-ID: <20181015120521.GA10146@redhat.com> References: 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 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Mon, 15 Oct 2018 12:05:33 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/12, Enke Chen wrote: > > For simplicity and consistency, this patch provides an implementation > for signal-based fault notification prior to the coredump of a child > process. A new prctl command, PR_SET_PREDUMP_SIG, is defined that can > be used by an application to express its interest and to specify the > signal (SIGCHLD or SIGUSR1 or SIGUSR2) for such a notification. A new > signal code (si_code), CLD_PREDUMP, is also defined for SIGCHLD. To be honest, I can't say I like this new feature... > --- a/include/linux/sched.h > +++ b/include/linux/sched.h > @@ -696,6 +696,10 @@ struct task_struct { > int exit_signal; > /* The signal sent when the parent dies: */ > int pdeath_signal; > + > + /* The signal sent prior to a child's coredump: */ > + int predump_signal; > + At least, I think predump_signal should live in signal_struct, not task_struct. (pdeath_signal too, but it is too late to change (fix) this awkward API). > +static void do_notify_parent_predump(struct task_struct *tsk) > +{ > + struct sighand_struct *sighand; > + struct task_struct *parent; > + struct kernel_siginfo info; > + unsigned long flags; > + int sig; > + > + parent = tsk->real_parent; So, debuggere won't be notified, only real_parent... > + sig = parent->predump_signal; probably ->predump_signal should be cleared on exec? > + /* Check again with tasklist_lock" locked by the caller */ > + if (!valid_predump_signal(sig)) > + return; I don't understand why we need valid_predump_signal() at all. > bool get_signal(struct ksignal *ksig) > { > struct sighand_struct *sighand = current->sighand; > @@ -2497,6 +2535,19 @@ bool get_signal(struct ksignal *ksig) > current->flags |= PF_SIGNALED; > > if (sig_kernel_coredump(signr)) { > + /* > + * Notify the parent prior to the coredump if the > + * parent is interested in such a notificaiton. > + */ > + int p_sig = current->real_parent->predump_signal; > + > + if (valid_predump_signal(p_sig)) { > + read_lock(&tasklist_lock); > + do_notify_parent_predump(current); > + read_unlock(&tasklist_lock); > + cond_resched(); perhaps this should be called by do_coredump() after coredump_wait() kills all the sub-threads? > +static int prctl_set_predump_signal(struct task_struct *tsk, pid_t pid, int sig) > +{ > + struct task_struct *p; > + int error; > + > + /* 0 is valid for disabling the feature */ > + if (sig && !valid_predump_signal(sig)) > + return -EINVAL; > + > + /* For the current task, the common case */ > + if (pid == 0) { > + tsk->predump_signal = sig; > + return 0; > + } > + > + error = -ESRCH; > + rcu_read_lock(); > + p = find_task_by_vpid(pid); > + if (p) { > + if (!set_predump_signal_perm(p)) > + error = -EPERM; > + else { > + error = 0; > + p->predump_signal = sig; > + } > + } > + rcu_read_unlock(); > + return error; > +} Why? I mean, why do we really want to support the pid != 0 case? Oleg.