Re: [PATCH 3/3] selftests/bpf: add memcg_stat_churn_percpu BPF-vs-memory.stat benchmark under cross-CPU churn

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Forked long-running child processes lack a parent-death signal, leading to runaway CPU-bound orphans if the test runner is forcefully terminated.
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commit 0078545540e155786a22dbc2aaffa44f31944e3b
Author: Ziyang Men <ziyang.meme@gmail.com>

selftests/bpf: add memcg_stat_churn_percpu BPF-vs-memory.stat benchmark under cross-CPU churn

This commit introduces a new test_progs benchmark to evaluate memory-cgroup
statistics reading under cross-CPU churn. It forks multiple churner child
processes that migrate across CPUs and constantly allocate and free memory.

> diff --git a/tools/testing/selftests/bpf/prog_tests/memcg_stat_churn_percpu.c b/tools/testing/selftests/bpf/prog_tests/memcg_stat_churn_percpu.c
> new file mode 100644
> index 0000000000000..16c3f261c8780
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/memcg_stat_churn_percpu.c

[ ... ]

> +static void churner_child(const struct cg_node *leaf, int base, int k,
> +			  size_t region_bytes, size_t resident_bytes)
> +{
> +	int c_pool = n_cpu - n_reserved;
> +	void *resident;
> +	int j = 0;

[ ... ]

> +	if (write(churn_ready[1], "x", 1) != 1)
> +		_exit(3);
> +	close(churn_ready[1]);	/* so a sibling's early death yields EOF, not a parent hang */
> +
> +	while (!ctl->stop) {
> +		void *p;
> +
> +		/* migrate to the next of our K CPUs, then dirty the leaf there */

[Severity: Medium]
Will these child processes run indefinitely as CPU-bound orphans if the test
runner is abruptly terminated?

Since the loop relies on the parent safely executing the cleanup path to set
ctl->stop = 1, a hard crash or a timeout (like a SIGKILL from a CI system)
could leave these processes running forever.

Would it make sense to call prctl(PR_SET_PDEATHSIG, SIGKILL) early in this
function so the kernel automatically cleans them up if the parent dies?

> +		pin_cpu(cpu_list[n_reserved + (base + j) % c_pool]);
> +		if (++j == k)
> +			j = 0;
> +
> +		p = mmap(NULL, region_bytes, PROT_READ | PROT_WRITE,
> +			 MAP_ANONYMOUS | MAP_PRIVATE, -1, 0);

[ ... ]

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Sashiko AI review · https://sashiko.dev/#/patchset/20260704045617.487664-1-ziyang.meme@gmail.com?part=3