linux-kernel - Re: [PATCH] trace-cmd: fix length calculation for padding events

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Date:	Thu, 26 Jan 2012 22:44:33 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	David Sharp <dhsharp@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mrubin@...gle.com, chavey@...gle.com,
	Gregory Haskins <gregory.haskins@...il.com>
Subject: Re: [PATCH] trace-cmd: fix length calculation for padding events

On Thu, 2012-01-26 at 19:00 -0800, David Sharp wrote:
> Padding events store size in bytes, not words. Usually this ends up pushing
> the parser off the current page, but occasionally not, and when not,
> it ends up desynchronizing the parser from the event stream. This would
> manifest as a lot of "ug!" messages from trace-cmd, and kernelshark
> crashing before displaying the UI.
> 

Nice! Funny, Gregory (Cc'd) sent me a trace.dat file that exhibited this
behavior. I was going to look into it tomorrow. I tried it with this
patch and it makes the bug go away.

Nice catch!  I wonder how long this has been around without notice?
Probably from day one.

-- Steve

> Signed-off-by: David Sharp <dhsharp@...gle.com>
> ---
>  trace-input.c |    1 -
>  1 files changed, 0 insertions(+), 1 deletions(-)
> 
> diff --git a/trace-input.c b/trace-input.c
> index e3157a7..b6af1e6 100644
> --- a/trace-input.c
> +++ b/trace-input.c
> @@ -1458,7 +1458,6 @@ translate_data(struct pevent *pevent,
>  	switch (type_len) {
>  	case RINGBUF_TYPE_PADDING:
>  		*length = data2host4(pevent, *ptr);
> -		*length *= 4;
>  		*ptr += *length;
>  		break;
>  


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