Re: [PATCH-cgroup/for-7.3] selftests/cgroup: Fix minor defects in test_cpuset

Michal Koutný <[email protected]> Mon, 20 Jul 2026 17:01:26 +0200

Newsgroups	org.kernel.vger.cgroups,org.kernel.vger.linux-kernel,org.kernel.vger.linux-kselftest
Message-ID	<[email protected]>

On Fri, Jul 17, 2026 at 03:18:14PM -0400, Waiman Long <[email protected]> wrote:
> With commit 98149f542530 ("selftests/cgroup: Add test for cpuset affinity
> on controller disable"), sashiko [1] had report 3 different issues with
> the new test_cpuset_affinity_on_controller_disable() test.
> 
>  1) `cpu_set_equal` iterates over mask bytes instead of bits, ignoring
>     CPUs >= 8.

Inline comment

>  2) Thread synchronization logic allows the main thread to read
>     uninitialized stack memory, causing test flakiness.

Hm, I cannot see it (alhtough I don't see it through), what was the
stack memory?
(test_phase is static, then re-initalized)

>  3) Test fails instead of skipping gracefully on uniprocessor systems
>     or when CPU 1 is unavailable.

Interesting catch.

> 
> Fix the reported issues by:
>  1) Iterates over the bit size of the mask.
>  2) Test the new ready flag for each thread to end the wait
>     on the condoitional variable and eliminate the now unneeded
>     AFFINITY_THREAD_A_READY and AFFINITY_THREADS_READY test phases.

But the symmetric synchronization with counter is easier to reason
about.

>  3) Return KSFT_SKIP on "cpuset.cpus" setting failure.

It'd be better to have same style with test_cpuset_prs.sh, i.e. a guard
at the beginning requesting a minimal number of CPUs. Next time...

> @@ -251,7 +251,7 @@ static int cpu_set_equal(cpu_set_t *dst, unsigned long mask)
>  	CPU_ZERO(&expected);
>  	assert(sizeof(mask) < CPU_SETSIZE);
>  
> -	for (int cpu = 0; cpu < sizeof(mask); ++cpu)
> +	for (int cpu = 0; cpu < sizeof(mask) * 8; ++cpu)
>  		if ((1UL << cpu) & mask)
>  			CPU_SET(cpu, &expected);

Oh, that was my braino in how masks are stored.
Thanks for correcting me!

It should also extend the assert accordingly:
  	assert(sizeof(mask) * 8 < CPU_SETSIZE);



Michal

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