Re: [LTP] getrusage03: Pin the test to a single CPU

[linuxtestproject.agent@gmail.com]

Hi Jan,

On Sep 4, 2026, Jan Stancek wrote:
> getrusage03: Pin the test to a single CPU

> +/*
> + * Pin the process (and everything it forks) to the CPU it currently runs on.
> + * Since commit f1a7941243c1 ("mm: convert mm's rss stats into percpu_counter")
> + * the RSS is tracked in a percpu counter whose fast read
> + * (percpu_counter_read_positive) only returns the global count, ignoring the
> + * per-CPU caches.

High: This setup makes the affected 100 MB child report pass instead of
exposing the approximately 64 MB getrusage(2) result. That is a kernel bug
workaround; keep the test migratable so the incorrect result remains visible.

> +	unsigned int cpu;
> +	cpu_set_t set;
> +
> +	if (getcpu(&cpu, NULL))
> +		tst_brk(TBROK | TERRNO, "getcpu() failed");
> +
> +	CPU_ZERO(&set);
> +	CPU_SET(cpu, &set);
> +	if (sched_setaffinity(0, sizeof(set), &set))
> +		tst_brk(TBROK | TERRNO, "sched_setaffinity() failed");

Medium: cpu_set_t cannot represent valid CPU IDs of CPU_SETSIZE or higher, so
CPU_SET() leaves the mask empty and sched_setaffinity() fails with EINVAL.
Use a dynamically allocated mask with CPU_ALLOC_SIZE(tst_ncpus_max()) and the
CPU_ZERO_S()/CPU_SET_S() interfaces.

Verdict - Needs revision

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