linux-kernel - Re: [PATCH] ring-buffer: fix uninitialized read

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Message-ID: <1340294204.27036.183.camel@gandalf.stny.rr.com>
Date:	Thu, 21 Jun 2012 11:56:44 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Sharp <dhsharp@...gle.com>
Cc:	linux-kernel@...r.kernel.org, vnagarnaik@...gle.com
Subject: Re: [PATCH] ring-buffer: fix uninitialized read_stamp

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.
 	 */


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