From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751908Ab0CHGuw (ORCPT ); Mon, 8 Mar 2010 01:50:52 -0500 Received: from cn.fujitsu.com ([222.73.24.84]:57152 "EHLO song.cn.fujitsu.com" rhost-flags-OK-FAIL-OK-OK) by vger.kernel.org with ESMTP id S1751034Ab0CHGur (ORCPT ); Mon, 8 Mar 2010 01:50:47 -0500 Message-ID: <4B949E43.2010906@cn.fujitsu.com> Date: Mon, 08 Mar 2010 14:50:43 +0800 From: Lai Jiangshan User-Agent: Thunderbird 2.0.0.6 (Windows/20070728) MIME-Version: 1.0 To: Ingo Molnar CC: Li Zefan , Steven Rostedt , Frederic Weisbecker , LKML Subject: Re: [BUG] WARNING: at kernel/trace/ring_buffer.c:3420 References: <4B94936B.8030409@cn.fujitsu.com> In-Reply-To: <4B94936B.8030409@cn.fujitsu.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Li Zefan wrote: > While running a ftrace test, a kernel warning showed up. The bug is not so > easy to reproduce, normally it takes 30 mins to 2 hours. > > After revering 3c05d7482777f15e71bb4cb1ba78dee2800dfec6, I ran the test > for 15 hours, and the bug seems disapeared. > This bug exhausted us, we found a issue: a tiny window which is one of causes of this bug. This patch is to close this tiny window. (bug is not fixed) From: Lai Jiangshan ringbuffer resizing and reseting will increase the ->record_disabled and then wait until a rcu_shced grace period passes. Contrarily, testing ->record_disabled should be at the same preempt disabled critical region as writing into ringbuffer, otherwise it will leave a window break ringbuffer resizing or reseting. Signed-off-by: Lai Jiangshan Reported-by: Li Zefan --- diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index 8c1b2d2..54191d6 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -2232,12 +2232,12 @@ ring_buffer_lock_reserve(struct ring_buffer *buffer, unsigned long length) if (ring_buffer_flags != RB_BUFFERS_ON) return NULL; - if (atomic_read(&buffer->record_disabled)) - return NULL; - /* If we are tracing schedule, we don't want to recurse */ resched = ftrace_preempt_disable(); + if (atomic_read(&buffer->record_disabled)) + goto out_nocheck; + if (trace_recursive_lock()) goto out_nocheck; @@ -2469,11 +2469,11 @@ int ring_buffer_write(struct ring_buffer *buffer, if (ring_buffer_flags != RB_BUFFERS_ON) return -EBUSY; - if (atomic_read(&buffer->record_disabled)) - return -EBUSY; - resched = ftrace_preempt_disable(); + if (atomic_read(&buffer->record_disabled)) + goto out; + cpu = raw_smp_processor_id(); if (!cpumask_test_cpu(cpu, buffer->cpumask))