Re: [PATCH v4 3/3] cgroup/cpuset: check sibling effective_xcpus in cpus_excl_conflict()

[Waiman Long <longman@redhat.com>]

On 9/24/26 12:27 AM, Hui Peng wrote:
> In cpus_excl_conflict(), when a valid local partition A1 uses implicit
> exclusive CPUs (cpuset.cpus set without cpuset.cpus.exclusive, so
> sibling->exclusive_cpus is empty while sibling->effective_xcpus is
> populated), a sibling cgroup B1 can still set cpuset.cpus.exclusive on
> the same CPUs because cpus_excl_conflict() only checks
> sibling->exclusive_cpus.
>
> Fall back to sibling->effective_xcpus in cpus_excl_conflict() when
> sibling->exclusive_cpus is empty, and add a regression test case to
> tools/testing/selftests/cgroup/test_cpuset_prs.sh.
>
> Tested in QEMU on Linux 7.3.0-rc3 using
> tools/testing/selftests/cgroup/test_cpuset_prs.sh.
>
> Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
>   kernel/cgroup/cpuset.c                            | 5 ++++-
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 1 +
>   2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 7c5b4a8f1f3a..f46a51f07938 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -713,7 +713,10 @@ static inline bool cpus_excl_conflict(struct cpuset *trial, struct cpuset *sibli
>   		return true;
>   
>   	/* Exclusive_cpus cannot intersect */
> -	return cpumask_intersects(trial->exclusive_cpus, sibling->exclusive_cpus);
> +	return cpumask_intersects(trial->exclusive_cpus,
> +				  cpumask_empty(sibling->exclusive_cpus)
> +				  ? sibling->effective_xcpus
> +				  : sibling->exclusive_cpus);
>   }
>   
>   static inline bool mems_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index f4d1822d4e21..f62155cf6162 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -445,6 +445,7 @@ TEST_MATRIX=(
>   
>   	# Changes to cpuset.cpus.exclusive that violate exclusivity rule is rejected
>   	"   C0-3     .      .    C4-5   X0-3     .      .     X3-5   1 A1:0-3|B1:4-5"
> +	"  C0-3:P1   .      .    C4-5     .      .      .     X3-5   1 A1:0-3|B1:4-5 A1:P1|B1:P0"
>   
>   	# cpuset.cpus.exclusive cannot be set to a superset of sibling's cpuset.cpus
>   	"   C0-3     .      .    C4-5   X3-5     .      .      .     1 A1:0-3|B1:4-5"
Reviewed-by: Waiman Long <longman@redhat.com>