Re: [PATCH-next v3 1/9] cgroup/cpuset: Fix a missing isolated_cpus update in update_cpumasks_hier()

[Guopeng Zhang <guopeng.zhang@linux.dev>]

在 2026/10/14 22:05, Waiman Long 写道:
> It is found that when a local isolated partition is being invalidated
> because its root partition parent is no longer valid, the isolated_cpus
> cpumask may not be properly updated. If the parent was previously
> an isolated partition, its invalidation should have properly updated
> isolated_cpus before and no action will be needed.
> 
> Fix that by calling isolated_cpus_update() in this invalidation case
> to update isolated_cpus. A test case in test_cpuset_prs.sh is modified
> to test that.
> 
> Fixes: 11e5f407b64a ("cgroup/cpuset: Keep track of CPUs in isolated partitions")
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
>  kernel/cgroup/cpuset.c                        | 19 ++++++++++++++-----
>  .../selftests/cgroup/test_cpuset_prs.sh       |  4 ++--
>  2 files changed, 16 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 0ebba2d646c3..6b5c870e5607 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2229,7 +2229,9 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>  		 * cpuset if the parent's effective_cpus changes.
>  		 */
>  		if ((cp != cs) && old_prs) {
> -			switch (parent->partition_root_state) {
> +			int parent_prs = parent->partition_root_state;
> +
> +			switch (parent_prs) {
>  			case PRS_ROOT:
>  			case PRS_ISOLATED:
>  				update_parent = true;
> @@ -2238,11 +2240,18 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
>  			default:
>  				/*
>  				 * When parent is not a partition root or is
> -				 * invalid, child partition roots become
> -				 * invalid too.
> +				 * invalid, child partition roots become invalid
> +				 * too. For an isolated partition with root
> +				 * partition parent, isolated_cpus_updated()
> +				 * is called to update isolated_cpus.
>  				 */
> -				if (is_partition_valid(cp))
> -					new_prs = -cp->partition_root_state;
> +				if (is_partition_valid(cp)) {
> +					new_prs = -old_prs;
> +					if ((old_prs == PRS_ISOLATED) &&
> +					    (parent_prs == -PRS_ROOT))
> +						isolated_cpus_update(old_prs, new_prs,
> +								     cp->effective_xcpus);
> +				}

I tested switching a parent partition from root to member and found that
CPUs can remain listed in cpuset.cpus.isolated. CPUs 0-15 are online, with
nohz_full=2-15 and no isolcpus:

    # cd /sys/fs/cgroup
    # echo +cpuset > cgroup.subtree_control
    # mkdir A
    # echo 1-2 > A/cpuset.cpus
    # echo root > A/cpuset.cpus.partition
    # echo +cpuset > A/cgroup.subtree_control
    # mkdir A/C
    # echo 2 > A/C/cpuset.cpus
    # echo isolated > A/C/cpuset.cpus.partition
    # cat cpuset.cpus.isolated
    2
    # echo member > A/cpuset.cpus.partition
    # cat A/C/cpuset.cpus.partition
    isolated invalid (Parent is not a partition root)
    # cat cpuset.cpus.isolated
    2

A is now a member and C is invalid, so cpuset.cpus.isolated should be
empty here, but CPU 2 remains.

Thanks,
Guopeng>  				WRITE_ONCE(cp->prs_err,
>  					   is_partition_invalid(parent)
>  					   ? PERR_INVPARENT : PERR_NOTPART);
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 7efd5e645767..874a8a161236 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -292,9 +292,9 @@ TEST_MATRIX=(
>  								       A1:P0|A2:P2|A3:P1 2-4|2-3"
>  	"   C0-4    C1-4  C2-4     .    X2-4  X2-4:P2 X3-4:P1   .    0 A1:0-1|A2:2|A3:3-4 \
>  								       A1:P0|A2:P2|A3:P1 2"
> -	" C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \
> +	" C0-4:X2-4 C1-4:X2-4:P1 C2-4:X4:P2 \
>  				   .      .      X5      .      .    0 A1:0-4|A2:1-4|A3:2-4 \
> -								       A1:P0|A2:P-2|A3:P-1 ."
> +								       A1:P0|A2:P-1|A3:P-2 ."
>  	" C0-4:X2-4 C1-4:X2-4:P2 C2-4:X4:P1 \
>  				   .      .      .      X1      .    0 A1:0-1|A2:2-4|A3:2-4 \
>  								       A1:P0|A2:P2|A3:P-1 2-4"