From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932405AbWDDJZX (ORCPT ); Tue, 4 Apr 2006 05:25:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S932407AbWDDJZX (ORCPT ); Tue, 4 Apr 2006 05:25:23 -0400 Received: from mx1.redhat.com ([66.187.233.31]:47334 "EHLO mx1.redhat.com") by vger.kernel.org with ESMTP id S932405AbWDDJZW (ORCPT ); Tue, 4 Apr 2006 05:25:22 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit From: Roland McGrath To: KaiGai Kohei X-Fcc: ~/Mail/linus Cc: Andrew Morton Cc: LKML Subject: Re: Fix pacct bug in multithreading case. In-Reply-To: KaiGai Kohei's message of Tuesday, 28 March 2006 20:43:49 +0900 <44292175.6030605@ak.jp.nec.com> X-Windows: it could be worse, but it'll take time. Message-Id: <20060404092507.753721809CE@magilla.sf.frob.com> Date: Tue, 4 Apr 2006 02:25:07 -0700 (PDT) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org That change looks correct to me, and I see that it's gone in. It made me think of another issue affecting the accounting records in related circumstances when the old group leader died after a non-leader exec. I think this patch addresses that, and along with your patch, gives more sensible times in all cases. Thanks, Roland [PATCH] Take original leader's start_time in non-leader exec. The only record we have of the real-time age of a process, regardless of execs it's done, is start_time. When a non-leader thread exec, the original start_time of the process is lost. Things looking at the real-time age of the process are fooled, for example the process accounting record when the process finally dies. This change makes the oldest start_time stick around with the process after a non-leader exec. This way the association between PID and start_time is kept constant, which seems correct to me. Signed-off-by: Roland McGrath --- fs/exec.c | 12 ++++++++++++ 1 files changed, 12 insertions(+), 0 deletions(-) 7cda52efb6ff969f049bc2ab3742b0341e45184a diff --git a/fs/exec.c b/fs/exec.c index 0291a68..a45f712 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -678,6 +678,18 @@ static int de_thread(struct task_struct while (leader->exit_state != EXIT_ZOMBIE) yield(); + /* + * The only record we have of the real-time age of a + * process, regardless of execs it's done, is start_time. + * All the past CPU time is accumulated in signal_struct + * from sister threads now dead. But in this non-leader + * exec, nothing survives from the original leader thread, + * whose birth marks the true age of this process now. + * When we take on its identity by switching to its PID, we + * also take its birthdate (always earlier than our own). + */ + current->start_time = leader->start_time; + spin_lock(&leader->proc_lock); spin_lock(¤t->proc_lock); proc_dentry1 = proc_pid_unhash(current); -- 1.2.4