From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756067Ab2FUP4r (ORCPT ); Thu, 21 Jun 2012 11:56:47 -0400 Received: from hrndva-omtalb.mail.rr.com ([71.74.56.122]:29036 "EHLO hrndva-omtalb.mail.rr.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755812Ab2FUP4q (ORCPT ); Thu, 21 Jun 2012 11:56:46 -0400 X-Authority-Analysis: v=2.0 cv=D8PF24tj c=1 sm=0 a=ZycB6UtQUfgMyuk2+PxD7w==:17 a=XQbtiDEiEegA:10 a=XOt6boVe9ZQA:10 a=5SG0PmZfjMsA:10 a=Q9fys5e9bTEA:10 a=meVymXHHAAAA:8 a=ayC55rCoAAAA:8 a=qi6N67ELxb11JToVk7kA:9 a=PUjeQqilurYA:10 a=ZycB6UtQUfgMyuk2+PxD7w==:117 X-Cloudmark-Score: 0 X-Originating-IP: 74.67.80.29 Message-ID: <1340294204.27036.183.camel@gandalf.stny.rr.com> Subject: Re: [PATCH] ring-buffer: fix uninitialized read_stamp From: Steven Rostedt To: David Sharp Cc: linux-kernel@vger.kernel.org, vnagarnaik@google.com Date: Thu, 21 Jun 2012 11:56:44 -0400 In-Reply-To: <1340293617.27036.177.camel@gandalf.stny.rr.com> References: <1340060577-9112-1-git-send-email-dhsharp@google.com> <1340293617.27036.177.camel@gandalf.stny.rr.com> Content-Type: text/plain; charset="ISO-8859-15" X-Mailer: Evolution 3.2.2-1+b1 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2012-06-21 at 11:46 -0400, Steven Rostedt wrote: > I'm wondering if it would be better to just not do the swap, and return > NULL when it is empty. This would also fix the problem, as the > read_stamp will only be set when you actually have data. Does something like this work for you. Note, this is totally untested! -- Steve diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c index ad0239b..5943044 100644 --- a/kernel/trace/ring_buffer.c +++ b/kernel/trace/ring_buffer.c @@ -3246,6 +3246,10 @@ rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer) if (cpu_buffer->commit_page == cpu_buffer->reader_page) goto out; + /* Don't bother swapping if the ring buffer is empty */ + if (rb_num_of_entries(cpu_buffer) == 0) + goto out; + /* * Reset the reader page to size zero. */