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

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Date:	Tue, 26 Jun 2012 17:35:34 -0700
From:	David Sharp <dhsharp@...gle.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	linux-kernel@...r.kernel.org, vnagarnaik@...gle.com
Subject: Re: [PATCH] ring-buffer: fix uninitialized read_stamp

On Fri, Jun 22, 2012 at 6:27 PM, David Sharp <dhsharp@...gle.com> wrote:
> On Fri, Jun 22, 2012 at 4:31 PM, Steven Rostedt <rostedt@...dmis.org> wrote:
>>
>> Now I think you may understand my patch.
>
> Yeah, mostly. At least enough that I think it's worth testing. But Monday.

I got around to testing your patch today, and it fixes the issue. No
bad-looking timestamps in 40 runs, whereas could reproduce within 3
runs before. Do you want me to send you a fresh patch, or just use the
one you have?

>>> On Thu, Jun 21, 2012 at 8:56 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
>>> > 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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