# Re: \[PATCH 1/2\] tracing/selftests: Fix instance test to actually test races

- From: Masami Hiramatsu (Google) \<mhiramat@kernel.org\>
- Date: 2026-10-30 01:01:22 
- List: linux-trace-kernel
- Page: https://ratatoskr.run/linux-trace-kernel/2026/10/17830133
- Thread: https://ratatoskr.run/linux-trace-kernel/2026/10/17829360/t.md

```text
On Thu, 29 Oct 2026 16:28:50 -0400, Steven Rostedt [ref] wrote:
> From: Steven Rostedt <rostedt@goodmis.org>
> 
> The instance selftest creates and removes the "foo" instance while
> enabling sched_switch event and reading its trace file. The issue is that
> the read of the trace file prevents the removal of foo, and it constantly
> fails to remove it. The stress test is not really stressing the situation.
> 
> Instead of running the creating and deletion in a loop as a separate
> process and sleeping for one second, call it directly in a loop that forces
> it to happen 10 times.  Also update the removal to keep trying until it
> removes the instance, otherwise if it doesn't remove it then the next mkdir
> is a nop.
> 
> Convert the reading of the trace file to use "head" instead of "cat" so it
> is limited in how much it reads and add a .1 sleep in between reads. This
> gives the removal of the instance time to succeed.
> 
> Fixes: 91e6f1ce86577 ("ftracetest: Add instance created, delete, read and enable event test")
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
>  .../ftrace/test.d/instances/instance-event.tc | 26 +++++++++----------
>  1 file changed, 12 insertions(+), 14 deletions(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc b/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc
> index 42422e425107..b0e9d3abbf2f 100644
> --- a/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc
> +++ b/tools/testing/selftests/ftrace/test.d/instances/instance-event.tc
> @@ -25,15 +25,16 @@ if [ $result -ne 0 ]; then
>  fi
>  
>  instance_slam() {
> -        while :; do
> -                mkdir foo 2> /dev/null
> -                rmdir foo 2> /dev/null
> -        done
> +	mkdir foo 2> /dev/null
> +	while ! rmdir foo; do
> +		echo could not rmdir foo

nit: If we retry this, do we need to warn it?
(maybe we can add a limitation of continuous failure and make the
test fail if the failure exceeds it.)

> +	done
>  }
>  

Thanks,

-- 
Masami Hiramatsu (Google) [ref]
```