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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id B6E6EC43334 for ; Wed, 22 Jun 2022 16:47:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1376672AbiFVQrv (ORCPT ); Wed, 22 Jun 2022 12:47:51 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:48146 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1376778AbiFVQr0 (ORCPT ); Wed, 22 Jun 2022 12:47:26 -0400 Received: from out01.mta.xmission.com (out01.mta.xmission.com [166.70.13.231]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 3473440A17 for ; Wed, 22 Jun 2022 09:46:33 -0700 (PDT) Received: from in02.mta.xmission.com ([166.70.13.52]:35050) by out01.mta.xmission.com with esmtps (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1o43Uu-004yHi-8f; Wed, 22 Jun 2022 10:46:32 -0600 Received: from ip68-227-174-4.om.om.cox.net ([68.227.174.4]:57374 helo=email.froward.int.ebiederm.org.xmission.com) by in02.mta.xmission.com with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.93) (envelope-from ) id 1o43Us-00FwBm-2Y; Wed, 22 Jun 2022 10:46:31 -0600 From: "Eric W. Biederman" To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, bigeasy@linutronix.de, Peter Zijlstra , Jann Horn , Kees Cook , Alexander Gordeev , Robert O'Callahan , Kyle Huey , Keno Fischer References: <20220421150248.667412396@infradead.org> <20220421150654.817117821@infradead.org> <87czhap9dy.fsf@email.froward.int.ebiederm.org> <878rrrh32q.fsf_-_@email.froward.int.ebiederm.org> <87k0b7v9yk.fsf_-_@email.froward.int.ebiederm.org> <87k0b0apne.fsf_-_@email.froward.int.ebiederm.org> <87a6bv6dl6.fsf_-_@email.froward.int.ebiederm.org> <87r13gd4xy.fsf_-_@email.froward.int.ebiederm.org> Date: Wed, 22 Jun 2022 11:46:23 -0500 In-Reply-To: <87r13gd4xy.fsf_-_@email.froward.int.ebiederm.org> (Eric W. Biederman's message of "Wed, 22 Jun 2022 11:43:37 -0500") Message-ID: <87bkukd4tc.fsf_-_@email.froward.int.ebiederm.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-XM-SPF: eid=1o43Us-00FwBm-2Y;;;mid=<87bkukd4tc.fsf_-_@email.froward.int.ebiederm.org>;;;hst=in02.mta.xmission.com;;;ip=68.227.174.4;;;frm=ebiederm@xmission.com;;;spf=softfail X-XM-AID: U2FsdGVkX1/WQCNlrCjNpy7h2EXBDC9Vav8tQ0hhtfU= X-SA-Exim-Connect-IP: 68.227.174.4 X-SA-Exim-Mail-From: ebiederm@xmission.com Subject: [PATCH 2/3] signal: Guarantee that SIGNAL_GROUP_EXIT is set on process exit X-SA-Exim-Version: 4.2.1 (built Sat, 08 Feb 2020 21:53:50 +0000) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Track how many threads have not started exiting and when the last thread starts exiting set SIGNAL_GROUP_EXIT. This guarantees that SIGNAL_GROUP_EXIT will get set when a process exits. In practice this achieves nothing as glibc's implementation of _exit calls sys_group_exit then sys_exit. While glibc's implemenation of pthread_exit calls exit (which cleansup and calls _exit) if it is the last thread and sys_exit if it is the last thread. This means the only way the kernel might observe a process that does not set call exit_group is if the language runtime does not use glibc. With more cleanups I hope to move the decrement of quick_threads earlier. Signed-off-by: "Eric W. Biederman" --- include/linux/sched/signal.h | 1 + kernel/exit.c | 18 ++++++++++++++++++ kernel/fork.c | 2 ++ 3 files changed, 21 insertions(+) diff --git a/include/linux/sched/signal.h b/include/linux/sched/signal.h index cafbe03eed01..20099268fa25 100644 --- a/include/linux/sched/signal.h +++ b/include/linux/sched/signal.h @@ -94,6 +94,7 @@ struct signal_struct { refcount_t sigcnt; atomic_t live; int nr_threads; + int quick_threads; struct list_head thread_head; wait_queue_head_t wait_chldexit; /* for wait4() */ diff --git a/kernel/exit.c b/kernel/exit.c index 96e4b12edea8..beaedb867bd3 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -733,11 +733,29 @@ static void check_stack_usage(void) static inline void check_stack_usage(void) {} #endif +static void synchronize_group_exit(struct task_struct *tsk, long code) +{ + struct sighand_struct *sighand = tsk->sighand; + struct signal_struct *signal = tsk->signal; + + spin_lock_irq(&sighand->siglock); + signal->quick_threads--; + if ((signal->quick_threads == 0) && + !(signal->flags & SIGNAL_GROUP_EXIT)) { + signal->flags = SIGNAL_GROUP_EXIT; + signal->group_exit_code = code; + signal->group_stop_count = 0; + } + spin_unlock_irq(&sighand->siglock); +} + void __noreturn do_exit(long code) { struct task_struct *tsk = current; int group_dead; + synchronize_group_exit(tsk, code); + WARN_ON(tsk->plug); kcov_task_exit(tsk); diff --git a/kernel/fork.c b/kernel/fork.c index 9d44f2d46c69..67813b25a567 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1692,6 +1692,7 @@ static int copy_signal(unsigned long clone_flags, struct task_struct *tsk) return -ENOMEM; sig->nr_threads = 1; + sig->quick_threads = 1; atomic_set(&sig->live, 1); refcount_set(&sig->sigcnt, 1); @@ -2444,6 +2445,7 @@ static __latent_entropy struct task_struct *copy_process( __this_cpu_inc(process_counts); } else { current->signal->nr_threads++; + current->signal->quick_threads++; atomic_inc(¤t->signal->live); refcount_inc(¤t->signal->sigcnt); task_join_group_stop(p); -- 2.35.3