Re: [PATCH] tracing: Fix trace_pipe_raw read panic

[Chunyu Hu]

A gentle ping. Any comment on this? Maybe have better solution for this?

On 25 July 2017 at 04:24, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> Hi Chunyu,
>
> Thanks for the patch. I'm currently traveling, and will have little
> time to test it. Hopefully I can get to it sometime this week.
>
> -- Steve
>
>
> On Mon, 24 Jul 2017 15:21:06 +0800
> Chunyu Hu <chuhu@xxxxxxxxxx> wrote:
>
>> per_cpu trace directories and files are created for all possible cpus,
>> but only the cpus which have ever been on-lined have their own per cpu
>> ring buffer (allocated by cpuhp threads). While trace_buffers_open, the
>> open handler for trace file 'trace_pipe_raw' is always trying to access
>> field of ring_buffer_per_cpu, and would panic with the NULL pointer.
>>
>> Align the behavior of trace_pipe_raw with trace_pipe, that returns -NODEV
>> when openning it if that cpu does not have trace ring buffer.
>>
>> Reproduce:
>> cat /sys/kernel/debug/tracing/per_cpu/cpu31/trace_pipe_raw
>> (cpu31 is never on-lined, this is a 16 cores x86_64 box)
>>
>> Tested with:
>> 1) boot with maxcpus=14, read trace_pipe_raw of cpu15.
>>    Got -NODEV.
>> 2) oneline cpu15, read trace_pipe_raw of cpu15.
>>    Get the raw trace data.