Re: [PATCH v1 03/12] perf tests workloads: Support sub-second durations in noploop and thloop

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Small sub-second durations or non-finite inputs (NaN/Infinity) truncate to zero and cancel the alarm, resulting in an infinite loop.
--

commit 00c5973576e890f274ed5c092471d3ff5f7e1ded
Author: Ian Rogers <irogers@google.com>

perf tests workloads: Support sub-second durations in noploop and thloop

This commit updates the noploop and thloop workloads to use atof() for
parsing the duration argument, allowing sub-second execution times. It uses
ualarm() for fractional durations under 1.0 second and falls back to
alarm() otherwise.

> diff --git a/tools/perf/tests/workloads/noploop.c b/tools/perf/tests/workloads/noploop.c
> --- a/tools/perf/tests/workloads/noploop.c
> +++ b/tools/perf/tests/workloads/noploop.c
[ ... ]
> @@ -15,15 +15,24 @@ static void sighandler(int sig __maybe_unused)
>  
>  static int noploop(int argc, const char **argv)
>  {
[ ... ]
> +	if (sec <= 0.0) {
> +		fprintf(stderr, "Error: seconds (%f) must be > 0\n", sec);
> +		return 1;
> +	}
>  
>  	signal(SIGINT, sighandler);
>  	signal(SIGALRM, sighandler);
> -	alarm(sec);
> +
> +	if (sec < 1.0)
> +		ualarm((useconds_t)(sec * 1000000.0), 0);
> +	else
> +		alarm((unsigned int)sec);

[Severity: Medium]
Could very small sub-second values or NaN inputs cause this to spin
infinitely?

If sec is NaN, the relational check sec <= 0.0 evaluates to false. Execution
falls through to the else block, casting NaN to unsigned int, which typically
results in 0 being passed to alarm().

Similarly, if sec is a very small positive value like 1e-7, it passes the
sec <= 0.0 error check. The calculation sec * 1000000.0 evaluates to 0.1,
which truncates to 0 when cast to useconds_t for ualarm().

Passing 0 to either alarm() or ualarm() cancels the timer entirely. Because
the timer is disabled, the signal handler is never invoked to set the done
flag, resulting in an infinite loop.

>  	while (!done)
>  		continue;
[ ... ]
> diff --git a/tools/perf/tests/workloads/thloop.c b/tools/perf/tests/workloads/thloop.c
> --- a/tools/perf/tests/workloads/thloop.c
> +++ b/tools/perf/tests/workloads/thloop.c
[ ... ]
> @@ -67,7 +68,10 @@ static int thloop(int argc, const char **argv)
>  			goto out;
>  		}
>  	}
> -	alarm(sec);
> +	if (sec < 1.0)
> +		ualarm((useconds_t)(sec * 1000000.0), 0);
> +	else
> +		alarm((unsigned int)sec);

[Severity: Medium]
Does this exhibit the same truncation to zero behavior with NaN or very small
sub-second inputs as the noploop workload?

>  	test_loop();
>  	err = 0;
>  out:

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260616012744.4049193-1-irogers@google.com?part=3