On 2023/8/12 03:25, Steven Rostedt wrote:

On Thu, 10 Aug 2023 20:39:05 +0800
Zheng Yejian [off-list ref] wrote:

quoted

When concurrently splice_read file trace_pipe and per_cpu/cpu*/trace_pipe,
there are more data being read out than expected.

Sorry, I didn't make clear here. It not just read more but also lost
some data. My case is that, for example:
   1) Inject 3 events into ring_buffer: event1, event2, event3;
   2) Concurrently splice_read through trace_pipes;
   3) Then actually read out: event1, event3, event3. No event2, but 2 
event3.

Honestly the real fix is to prevent that use case. We should probably have
access to trace_pipe lock all the per_cpu trace_pipes too.

Yes, we could do that, but would it seem not that effective?
because per_cpu trace_pipe only read its own ring_buffer and not race
with ring_buffers in other cpus.

-- Steve