From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752864AbYKRMyR (ORCPT ); Tue, 18 Nov 2008 07:54:17 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751671AbYKRMyE (ORCPT ); Tue, 18 Nov 2008 07:54:04 -0500 Received: from mtagate7.de.ibm.com ([195.212.29.156]:40400 "EHLO mtagate7.de.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751127AbYKRMyC (ORCPT ); Tue, 18 Nov 2008 07:54:02 -0500 Date: Tue, 18 Nov 2008 13:54:00 +0100 From: Heiko Carstens To: Steven Rostedt Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Martin Schwidefsky Subject: ftrace: preemptoff selftest not working Message-ID: <20081118125359.GA4417@osiris.boeblingen.de.ibm.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 Hi Steven, I was wondering why the preemptoff and preemptirqsoff tracer selftests don't work on s390. After all its just that they get called from non-preemptible context: kernel_init() will execute all initcalls, however the first line in kernel_init() is lock_kernel(), which causes the preempt_count to be increased. Any later calls to add_preempt_count() (especially those from the selftests) will therefore not result in a call to trace_preempt_off() since the check below in add_preempt_count() will be false: if (preempt_count() == val) trace_preempt_off(CALLER_ADDR0, get_parent_ip(CALLER_ADDR1)); Hence the trace buffer will be empty. The patch below makes the selftests working for me, since then they run in preemptible context. But it is ugly and I'm not proposing it for upstream ;) Just wanted to make you aware that there is a bug. --- init/main.c | 4 ++++ kernel/trace/trace_irqsoff.c | 3 +-- 2 files changed, 5 insertions(+), 2 deletions(-) Index: linux-2.6/kernel/trace/trace_irqsoff.c =================================================================== --- linux-2.6.orig/kernel/trace/trace_irqsoff.c +++ linux-2.6/kernel/trace/trace_irqsoff.c @@ -482,7 +482,7 @@ static struct tracer preemptirqsoff_trac # define register_preemptirqsoff(trace) do { } while (0) #endif -__init static int init_irqsoff_tracer(void) +int init_irqsoff_tracer(void) { register_irqsoff(irqsoff_tracer); register_preemptoff(preemptoff_tracer); @@ -490,4 +490,3 @@ __init static int init_irqsoff_tracer(vo return 0; } -device_initcall(init_irqsoff_tracer); Index: linux-2.6/init/main.c =================================================================== --- linux-2.6.orig/init/main.c +++ linux-2.6/init/main.c @@ -789,6 +789,8 @@ static void run_init_process(char *init_ kernel_execve(init_filename, argv_init, envp_init); } +extern int init_irqsoff_tracer(void); + /* This is a non __init function. Force it to be noinline otherwise gcc * makes it inline to init() and it becomes part of init.text section */ @@ -800,6 +802,8 @@ static int noinline init_post(void) system_state = SYSTEM_RUNNING; numa_default_policy(); + init_irqsoff_tracer(); + if (sys_open((const char __user *) "/dev/console", O_RDWR, 0) < 0) printk(KERN_WARNING "Warning: unable to open an initial console.\n");