Re: [PATCH] selftests/tracing: Fix false failure of subsystem event test

[Steven Rostedt]

Shuah,

Can you take this patch?

Thanks,

-- Steve


On Mon, 21 Jul 2025 13:42:12 -0400
Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:

> From: Steven Rostedt <rostedt@xxxxxxxxxxx>
> 
> The subsystem event test enables all "sched" events and makes sure there's
> at least 3 different events in the output. It used to cat the entire trace
> file to | wc -l, but on slow machines, that could last a very long time.
> To solve that, it was changed to just read the first 100 lines of the
> trace file. This can cause false failures as some events repeat so often,
> that the 100 lines that are examined could possibly be of only one event.
> 
> Instead, create an awk script that looks for 3 different events and will
> exit out after it finds them. This will find the 3 events the test looks
> for (eventually if it works), and still exit out after the test is
> satisfied and not cause slower machines to run forever.
> 
> Reported-by: Tengda Wu <wutengda@xxxxxxxxxxxxxxx>
> Closes: https://lore.kernel.org/all/20250710130134.591066-1-wutengda@xxxxxxxxxxxxxxx/
> Fixes: 1a4ea83a6e67 ("selftests/ftrace: Limit length in subsystem-enable tests")
> Signed-off-by: Steven Rostedt (Google) <rostedt@xxxxxxxxxxx>
> ---
>  .../ftrace/test.d/event/subsystem-enable.tc   | 28 +++++++++++++++++--
>  1 file changed, 26 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/testing/selftests/ftrace/test.d/event/subsystem-enable.tc b/tools/testing/selftests/ftrace/test.d/event/subsystem-enable.tc
> index b7c8f29c09a9..65916bb55dfb 100644
> --- a/tools/testing/selftests/ftrace/test.d/event/subsystem-enable.tc
> +++ b/tools/testing/selftests/ftrace/test.d/event/subsystem-enable.tc
> @@ -14,11 +14,35 @@ fail() { #msg
>      exit_fail
>  }
>  
> +# As reading trace can last forever, simply look for 3 different
> +# events then exit out of reading the file. If there's not 3 different
> +# events, then the test has failed.
> +check_unique() {
> +    cat trace | grep -v '^#' | awk '
> +	BEGIN { cnt = 0; }
> +	{
> +	    for (i = 0; i < cnt; i++) {
> +		if (event[i] == $5) {
> +		    break;
> +		}
> +	    }
> +	    if (i == cnt) {
> +		event[cnt++] = $5;
> +		if (cnt > 2) {
> +		    exit;
> +		}
> +	    }
> +	}
> +	END {
> +	    printf "%d", cnt;
> +	}'
> +}
> +
>  echo 'sched:*' > set_event
>  
>  yield
>  
> -count=`head -n 100 trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
> +count=`check_unique`
>  if [ $count -lt 3 ]; then
>      fail "at least fork, exec and exit events should be recorded"
>  fi
> @@ -29,7 +53,7 @@ echo 1 > events/sched/enable
>  
>  yield
>  
> -count=`head -n 100 trace | grep -v ^# | awk '{ print $5 }' | sort -u | wc -l`
> +count=`check_unique`
>  if [ $count -lt 3 ]; then
>      fail "at least fork, exec and exit events should be recorded"
>  fi