Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753071AbaBXT1r (ORCPT ); Mon, 24 Feb 2014 14:27:47 -0500 Received: from smtp3-g21.free.fr ([212.27.42.3]:37098 "EHLO smtp3-g21.free.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752495AbaBXT1q (ORCPT ); Mon, 24 Feb 2014 14:27:46 -0500 Date: Mon, 24 Feb 2014 20:27:34 +0100 From: Guillaume Morin To: matt.helsley@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org Cc: linux-kernel@vger.kernel.org Subject: [PATCH] exit.c: call proc_exit_connector() after exit_state is set Message-ID: <20140224192734.GA15573@bender.morinfr.org> Mail-Followup-To: matt.helsley@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Guillaume Morin The process events connector delivers a notification when a process exits. This is really convenient for a process that spawns and wants to monitor its children through an epoll-able() interface. Unfortunately, there is a small window between when the event is delivered and the child become wait()-able. This is creates a race if the parent wants to make sure that it knows about the exit, e.g pid_t pid = fork(); if (pid > 0) { register_interest_for_pid(pid); if (waitpid(pid, NULL, WNOHANG) > 0) { /* We might have raced with exit() */ } return; } /* Child */ execve(...) register_interest_for_pid() would be telling the the connector socket reader to pay attention to events related to pid. Though this is not a bug, I think it would make the connector a bit more usable if this race was closed by simply moving the call to proc_exit_connector() from just before exit_notify() to right after. Signed-off-by: Guillaume Morin Cc: matt.helsley@gmail.com --- diff --git a/kernel/exit.c b/kernel/exit.c index 1e77fc6..9b0ac8c 100644 --- a/kernel/exit.c +++ b/kernel/exit.c @@ -804,7 +804,6 @@ void do_exit(long code) module_put(task_thread_info(tsk)->exec_domain->module); - proc_exit_connector(tsk); /* * FIXME: do that only when needed, using sched_exit tracepoint @@ -812,6 +811,7 @@ void do_exit(long code) flush_ptrace_hw_breakpoint(tsk); exit_notify(tsk, group_dead); + proc_exit_connector(tsk); #ifdef CONFIG_NUMA task_lock(tsk); mpol_put(tsk->mempolicy); -- Guillaume Morin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/