Re: [PATCH 2/2] selftests/sched_ext: Verify nohz_full tick behavior

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Worker processes will spin indefinitely if the test terminates abnormally.
--

commit 5f5f7d1cf8a2f7b2edb91658dc637840224ea1dd
Author: Andrea Righi <arighi@nvidia.com>

selftests/sched_ext: Verify nohz_full tick behavior

This commit adds a regression test to validate proper nohz_full behavior in
sched_ext. It verifies that a finite-slice EXT task restarts the periodic
scheduler tick when it follows an infinite-slice task on a NOHZ_FULL CPU.

> diff --git a/tools/testing/selftests/sched_ext/nohz_tick.c b/tools/testing/selftests/sched_ext/nohz_tick.c
> new file mode 100644
> --- /dev/null
> +++ b/tools/testing/selftests/sched_ext/nohz_tick.c

[ ... ]

> +static pid_t start_worker(int cpu)
> +{
> +	struct sched_param param = {};
> +	cpu_set_t mask;
> +	pid_t pid;
> +
> +	pid = fork();
> +	if (pid != 0)
> +		return pid;
> +
> +	/*
> +	 * Become EXT before touching the target so it stays idle until wakeup.
> +	 */
> +	if (sched_setscheduler(0, SCHED_EXT, &param))
> +		_exit(1);
> +
> +	CPU_ZERO(&mask);
> +	CPU_SET(cpu, &mask);
> +	if (sched_setaffinity(0, sizeof(mask), &mask))
> +		_exit(1);
> +
> +	for (;;)
> +		asm volatile("" ::: "memory");

[Severity: Medium]
If the test runner terminates abnormally before reaching stop_worker(), will
this orphaned child process continue to spin indefinitely?

Since the child runs under the SCHED_EXT policy and is pinned to a specific
CPU, an orphaned child would consume 100% of that CPU indefinitely and
potentially interfere with subsequent tests.

Would it be safer to use prctl(PR_SET_PDEATHSIG, SIGKILL) after forking so
the worker is automatically killed if the parent test process exits
unexpectedly?

[ ... ]

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260706162819.650155-1-arighi@nvidia.com?part=2