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SubjectRe: Mmiotrace regression in 2.6.28-rc6

On Sun, 23 Nov 2008, Pekka Paalanen wrote:

> Hi Steve,
>
> now that the NULL deref bug in ring buffer resize is gone, I found
> another regression.
>
> It seems I am not getting any "buffer overflow" messages anymore.
>
> Oh bummer, looks like I completely missed this one:
> (hope it's not in any .27 kernel)
>
>
> commit 3928a8a2d98081d1bc3c0a84a2d70e29b90ecf1c
> Author: Steven Rostedt <rostedt@goodmis.org>
> Date: Mon Sep 29 23:02:41 2008 -0400
>
> ftrace: make work with new ring buffer
>
> This patch ports ftrace over to the new ring buffer.
>
> Signed-off-by: Steven Rostedt <srostedt@redhat.com>
> Signed-off-by: Ingo Molnar <mingo@elte.hu>
>
> <...>
> diff --git a/kernel/trace/trace_mmiotrace.c b/kernel/trace/trace_mmiotrace.c
> index a108c32..bdbf09d 100644
> --- a/kernel/trace/trace_mmiotrace.c
> +++ b/kernel/trace/trace_mmiotrace.c
> <...>
> @@ -130,10 +130,14 @@ static unsigned long count_overruns(struct trace_iterator *iter)
> {
> int cpu;
> unsigned long cnt = 0;
> +/* FIXME: */
> +#if 0
> for_each_online_cpu(cpu) {
> cnt += iter->overrun[cpu];
> iter->overrun[cpu] = 0;
> }
> +#endif

Hi Pekka,

Use ring_buffer_overruns(iter->tr->buffer). See print_trace_hader in
kernel/trace/trace.c for more info.


-- Steve


> + (void)cpu;
> return cnt;
> }
>
> Steve, how am I going to fix this?
> I think it's quite crucial to know when the dump is incomplete.
>
>
> There's also another issue, but I am not sure how to reproduce it.
> The symptom is, that
> echo whatever > /debug/tracing/trace_marker
> gets stuck in a loop, bash eats 100% CPU: 10% user, 90% system.
> I got that twice today, like this: after a fresh boot echoing 64, 200,
> 70 to trace_entries, switching between nop and mmiotrace tracers,
> echoing 0 or 1 to tracing_enabled, and running the testmmiotrace
> module. At some point the user marker got stuck.
>
> But then I tried to do that a third time by repeating some usage
> patterns I thought might trigger it, but it didn't happen.
>
> On the positive side, the basic test using testmmiotrace.ko
> with the basic setup produces the correct output.
>
>
> Thanks.
>
> --
> Pekka Paalanen
> http://www.iki.fi/pq/
>
>


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