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 D97D3C43387 for ; Tue, 8 Jan 2019 16:50:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9D9E2087F for ; Tue, 8 Jan 2019 16:50:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728403AbfAHQuq (ORCPT ); Tue, 8 Jan 2019 11:50:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33968 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727484AbfAHQuq (ORCPT ); Tue, 8 Jan 2019 11:50:46 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id D9A4280F91; Tue, 8 Jan 2019 16:50:45 +0000 (UTC) Received: from dhcp-27-174.brq.redhat.com (unknown [10.43.17.103]) by smtp.corp.redhat.com (Postfix) with SMTP id 7C33D18EF3; Tue, 8 Jan 2019 16:50:44 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 8 Jan 2019 17:50:45 +0100 (CET) Date: Tue, 8 Jan 2019 17:50:43 +0100 From: Oleg Nesterov To: Andrei Vagin Cc: Alexander Viro , Andrew Morton , linux-kernel@vger.kernel.org, "Eric W. Biederman" Subject: Re: [PATCH] kernel: release ptraced tasks before zap_pid_ns_processes Message-ID: <20190108165043.GA10240@redhat.com> References: <20190102205939.26231-1-avagin@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190102205939.26231-1-avagin@gmail.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Tue, 08 Jan 2019 16:50:46 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Sorry for delay, vacation, On 01/02, Andrei Vagin wrote: > > zap_pid_ns_processes() can stuck on waiting tasks from the dead list. In > this case, we will have one unkillable process with one or more dead > children. Thanks! > --- a/kernel/exit.c > +++ b/kernel/exit.c > @@ -664,9 +664,6 @@ static void forget_original_parent(struct task_struct *father, > { > struct task_struct *p, *t, *reaper; > > - if (unlikely(!list_empty(&father->ptraced))) > - exit_ptrace(father, dead); > - > /* Can drop and reacquire tasklist_lock */ > reaper = find_child_reaper(father); > if (list_empty(&father->children)) > @@ -705,8 +702,18 @@ static void exit_notify(struct task_struct *tsk, int group_dead) > LIST_HEAD(dead); > > write_lock_irq(&tasklist_lock); > - forget_original_parent(tsk, &dead); > + if (unlikely(!list_empty(&tsk->ptraced))) > + exit_ptrace(tsk, &dead); > + write_unlock_irq(&tasklist_lock); > + > + /* Ptraced tasks have to be released before zap_pid_ns_processes(). */ > + list_for_each_entry_safe(p, n, &dead, ptrace_entry) { > + list_del_init(&p->ptrace_entry); > + release_task(p); > + } > > + write_lock_irq(&tasklist_lock); > + forget_original_parent(tsk, &dead); > if (group_dead) > kill_orphaned_pgrp(tsk->group_leader, NULL); How about a different fix below? It avoids additional write_lock/unlock(tasklist), and another list_for_each_entry_safe(dead) loop is called only if it is actually needed. Or I missed something? Oleg. --- x/kernel/exit.c +++ x/kernel/exit.c @@ -558,12 +558,14 @@ static struct task_struct *find_alive_th return NULL; } -static struct task_struct *find_child_reaper(struct task_struct *father) +static struct task_struct *find_child_reaper(struct task_struct *father, + struct list_head *dead) __releases(&tasklist_lock) __acquires(&tasklist_lock) { struct pid_namespace *pid_ns = task_active_pid_ns(father); struct task_struct *reaper = pid_ns->child_reaper; + struct task_struct *p, *n; if (likely(reaper != father)) return reaper; @@ -579,6 +581,11 @@ static struct task_struct *find_child_re panic("Attempted to kill init! exitcode=0x%08x\n", father->signal->group_exit_code ?: father->exit_code); } + + list_for_each_entry_safe(p, n, &dead, ptrace_entry) { + list_del_init(&p->ptrace_entry); + release_task(p); + } zap_pid_ns_processes(pid_ns); write_lock_irq(&tasklist_lock); @@ -668,7 +675,7 @@ static void forget_original_parent(struc exit_ptrace(father, dead); /* Can drop and reacquire tasklist_lock */ - reaper = find_child_reaper(father); + reaper = find_child_reaper(father, dead); if (list_empty(&father->children)) return;