From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751581Ab0CRSzS (ORCPT ); Thu, 18 Mar 2010 14:55:18 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43254 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751323Ab0CRSzJ (ORCPT ); Thu, 18 Mar 2010 14:55:09 -0400 Date: Thu, 18 Mar 2010 19:53:04 +0100 From: Oleg Nesterov To: Andrew Morton Cc: Fenghua Yu , Roland McGrath , Stanislaw Gruszka , Tony Luck , linux-kernel@vger.kernel.org Subject: [PATCH 1/2] posix-cpu-timers: avoid "task->signal != NULL" checks Message-ID: <20100318185304.GA18348@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org No functional changes. posix-cpu-timers.c checks task->signal != NULL to ensure this task is alive and didn't pass __exit_signal(). This is correct but we are going to change the lifetime rules for ->signal and never reset this pointer. Change the code to check ->sighand instead, it doesn't matter which pointer we check under tasklist, they both are cleared simultaneously. As Roland pointed out, some of these changes are not strictly needed and probably it makes sense to revert them later, when ->signal will be pinned to task_struct. But this patch tries to ensure the subsequent changes in fork/exit can't make any visible impact on posix cpu timers. Signed-off-by: Oleg Nesterov --- kernel/posix-cpu-timers.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) --- 34-rc1/kernel/posix-cpu-timers.c~5_PCT_DONT_CHECK_SIGNAL 2010-03-11 13:11:50.000000000 +0100 +++ 34-rc1/kernel/posix-cpu-timers.c 2010-03-18 17:49:17.000000000 +0100 @@ -364,7 +364,7 @@ int posix_cpu_clock_get(const clockid_t } } else { read_lock(&tasklist_lock); - if (thread_group_leader(p) && p->signal) { + if (thread_group_leader(p) && p->sighand) { error = cpu_clock_sample_group(which_clock, p, &rtn); @@ -440,7 +440,7 @@ int posix_cpu_timer_del(struct k_itimer if (likely(p != NULL)) { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * We raced with the reaping of the task. * The deletion should have cleared us off the list. @@ -736,10 +736,10 @@ int posix_cpu_timer_set(struct k_itimer read_lock(&tasklist_lock); /* * We need the tasklist_lock to protect against reaping that - * clears p->signal. If p has just been reaped, we can no + * clears p->sighand. If p has just been reaped, we can no * longer get any information about it at all. */ - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { read_unlock(&tasklist_lock); put_task_struct(p); timer->it.cpu.task = NULL; @@ -908,7 +908,7 @@ void posix_cpu_timer_get(struct k_itimer clear_dead = p->exit_state; } else { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * The process has been reaped. * We can't even collect a sample any more. @@ -1268,7 +1268,7 @@ void posix_cpu_timer_schedule(struct k_i read_lock(&tasklist_lock); /* arm_timer needs it. */ } else { read_lock(&tasklist_lock); - if (unlikely(p->signal == NULL)) { + if (unlikely(p->sighand == NULL)) { /* * The process has been reaped. * We can't even collect a sample any more.