Re: [PATCH v2] cpuset: relax the overlap check for cgroup-v2

[Waiman Long <llong@redhat.com>]

On 11/13/25 8:14 AM, Sun Shaojie wrote:
> In cgroup v2, a mutual overlap check is required when at least one of two
> cpusets is exclusive. However, this check should be relaxed and limited to
> cases where both cpusets are exclusive.
>
> The table 1 shows the partition states of A1 and B1 after each step before
> applying this patch.
>
> Table 1: Before applying the patch
>   Step                                       | A1's prstate | B1's prstate |
>   #1> mkdir -p A1                            | member       |              |
>   #2> echo "0-1" > A1/cpuset.cpus            | member       |              |
>   #3> echo "root" > A1/cpuset.cpus.partition | root         |              |
>   #4> mkdir -p B1                            | root         | member       |
>   #5> echo "0-3" > B1/cpuset.cpus            | root invalid | member       |
>   #6> echo "root" > B1/cpuset.cpus.partition | root invalid | root invalid |
>
> After step #5, A1 changes from "root" to "root invalid" because its CPUs
> (0-1) overlap with those requested by B1 (0-3). However, B1 can actually
> use CPUs 2-3, so it would be more reasonable for A1 to remain as "root."
>
> This patch relaxes the exclusive cpuset check for cgroup v2 while
> preserving the current cgroup v1 behavior.
>
> Signed-off-by: Sun Shaojie <sunshaojie@kylinos.cn>
>
> ---
> v1 -> v2:
>    - Keeps the current cgroup v1 behavior unchanged
>    - Link: https://lore.kernel.org/cgroups/c8e234f4-2c27-4753-8f39-8ae83197efd3@redhat.com
> ---
>   kernel/cgroup/cpuset.c                            |  9 +++++++--
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 10 +++++-----
>   2 files changed, 12 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 52468d2c178a..3240b3ab5998 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -592,8 +592,13 @@ static inline bool cpusets_are_exclusive(struct cpuset *cs1, struct cpuset *cs2)
>    */
>   static inline bool cpus_excl_conflict(struct cpuset *cs1, struct cpuset *cs2)
>   {
> -	/* If either cpuset is exclusive, check if they are mutually exclusive */
> -	if (is_cpu_exclusive(cs1) || is_cpu_exclusive(cs2))
> +	/* If both cpusets are exclusive, check if they are mutually exclusive */
> +	if (is_cpu_exclusive(cs1) && is_cpu_exclusive(cs2))
> +		return !cpusets_are_exclusive(cs1, cs2);
> +
> +	/* In cgroup-v1, if either cpuset is exclusive, check if they are mutually exclusive */
> +	if (!is_in_v2_mode() &&

You should just use cpuset_v2() here as is_in_v2_mode() checks an 
additional v1 specific mode that is irrelevant wrt to exclusive bit 
handling. Also please update the functional comment about difference in 
v1 vs. v2 behavior.

Note that we may have to update other conflict checking code in cpuset.c 
to make this new behavior more consistent.

Thanks,
Longman

> +	    (is_cpu_exclusive(cs1) != is_cpu_exclusive(cs2)))
>   		return !cpusets_are_exclusive(cs1, cs2);
>   
>   	/* Exclusive_cpus cannot intersect */
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index a17256d9f88a..903dddfe88d7 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -269,7 +269,7 @@ TEST_MATRIX=(
>   	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X3:P2    .      .     0 A1:0-2|A2:3|A3:3 A1:P0|A2:P2 3"
>   	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X2-3  X2-3:P2   .     0 A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
>   	" C0-3:S+ C1-3:S+ C2-3     .    X2-3   X2-3 X2-3:P2:C3 .     0 A1:0-1|A2:1|A3:2-3 A1:P0|A3:P2 2-3"
> -	" C0-3:S+ C1-3:S+ C2-3   C2-3     .      .      .      P2    0 A1:0-3|A2:1-3|A3:2-3|B1:2-3 A1:P0|A3:P0|B1:P-2"
> +	" C0-3:S+ C1-3:S+ C2-3   C2-3     .      .      .      P2    0 A1:0-1|A2:1|A3:1|B1:2-3 A1:P0|A3:P0|B1:P2 2-3"
>   	" C0-3:S+ C1-3:S+ C2-3   C4-5     .      .      .      P2    0 B1:4-5 B1:P2 4-5"
>   	" C0-3:S+ C1-3:S+ C2-3    C4    X2-3   X2-3  X2-3:P2   P2    0 A3:2-3|B1:4 A3:P2|B1:P2 2-4"
>   	" C0-3:S+ C1-3:S+ C2-3    C4    X2-3   X2-3 X2-3:P2:C1-3 P2  0 A3:2-3|B1:4 A3:P2|B1:P2 2-4"
> @@ -318,7 +318,7 @@ TEST_MATRIX=(
>   	# Invalid to valid local partition direct transition tests
>   	" C1-3:S+:P2 X4:P2  .      .      .      .      .      .     0 A1:1-3|XA1:1-3|A2:1-3:XA2: A1:P2|A2:P-2 1-3"
>   	" C1-3:S+:P2 X4:P2  .      .      .    X3:P2    .      .     0 A1:1-2|XA1:1-3|A2:3:XA2:3 A1:P2|A2:P2 1-3"
> -	"  C0-3:P2   .      .    C4-6   C0-4     .      .      .     0 A1:0-4|B1:4-6 A1:P-2|B1:P0"
> +	"  C0-3:P2   .      .    C4-6   C0-4     .      .      .     0 A1:0-4|B1:5-6 A1:P2|B1:P0 0-4"
>   	"  C0-3:P2   .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
>   
>   	# Local partition invalidation tests
> @@ -388,10 +388,10 @@ TEST_MATRIX=(
>   	"  C0-1:S+  C1      .    C2-3     .      P2     .      .     0 A1:0-1|A2:1 A1:P0|A2:P-2"
>   	"  C0-1:S+ C1:P2    .    C2-3     P1     .      .      .     0 A1:0|A2:1 A1:P1|A2:P2 0-1|1"
>   
> -	# A non-exclusive cpuset.cpus change will invalidate partition and its siblings
> -	"  C0-1:P1   .      .    C2-3   C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P-1|B1:P0"
> +	# A non-exclusive cpuset.cpus change will not invalidate partition and its siblings
> +	"  C0-1:P1   .      .    C2-3   C0-2     .      .      .     0 A1:0-2|B1:3 A1:P1|B1:P0"
>   	"  C0-1:P1   .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P-1|B1:P-1"
> -	"   C0-1     .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-2|B1:2-3 A1:P0|B1:P-1"
> +	"   C0-1     .      .  P1:C2-3  C0-2     .      .      .     0 A1:0-1|B1:2-3 A1:P0|B1:P1"
>   
>   	# cpuset.cpus can overlap with sibling cpuset.cpus.exclusive but not subsumed by it
>   	"   C0-3     .      .    C4-5     X5     .      .      .     0 A1:0-3|B1:4-5"