* [PATCH-next] cgroup/cpuset: Fix incorrect CPU accounting with parent's effective_xcpus expansion
@ 2026-10-28 15:26 Waiman Long
2026-10-29 9:42 ` Guopeng Zhang
0 siblings, 1 reply; 3+ messages in thread
From: Waiman Long @ 2026-10-28 15:26 UTC (permalink / raw)
To: Ridong Chen, Tejun Heo, Johannes Weiner, Michal Koutný,
Shuah Khan
Cc: cgroups, linux-kernel, linux-kselftest, Guopeng Zhang,
Waiman Long
Commit ec0254b9eb49 ("cgroup/cpuset: Release invalid isolated CPUs with
a shrunk root partition parent") fixes incorrect isolated_cpus accounting
when contraction of a parent's effective_xcpus can cause a child partition
to lose isolated CPUs. Expansion of parent's effective_cpus can also allow
a child partition to gain more effective_xcpus. However, the current code
doesn't handle this case correctly leading to incorrect effective_cpus
and isolated_cpus accounting. Fix that by looking for this possible
expansion of effective_xcpus and perform the proper accounting action.
New test cases are added to test this effective_xcpus expansion scenarios.
Reported-by: Guopeng Zhang <guopeng.zhang@linux.dev>
Link: https://lore.kernel.org/lkml/20261027123837.100909-1-guopeng.zhang@linux.dev
Signed-off-by: Waiman Long <longman@redhat.com>
---
kernel/cgroup/cpuset.c | 12 ++++++++++++
tools/testing/selftests/cgroup/test_cpuset_prs.sh | 15 +++++++++++++++
2 files changed, 27 insertions(+)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 3219f927c35e..39c81a0a8ab9 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2097,6 +2097,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
parent->effective_xcpus);
if (!cpumask_empty(tmp->addmask))
isolated_cpus_release(cs, tmp->addmask);
+ /* Expansion of parent's effective_xcpus is handled below */
}
if (nocpu) {
part_error = PERR_NOCPUS;
@@ -2106,11 +2107,22 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
parent->effective_xcpus);
} else if ((parent_prs == PRS_ISOLATED) &&
((old_prs == PRS_ROOT) || (old_prs == -PRS_ROOT))) {
+ /* Parent partition state changed to PRS_ISOLATED */
part_error = PERR_ISOPARENT;
if (old_prs == PRS_ROOT) {
cpumask_copy(tmp->addmask, cs->effective_xcpus);
adding = true;
}
+ } else if (is_partition_valid(cs) &&
+ !cpumask_equal(tmp->delmask, cs->effective_xcpus)) {
+ /*
+ * If there is an expansion of parent's effective_xcpus,
+ * we may take more xcpus from parent. The parent's
+ * effective_cpus should still have active CPUs or nocpu
+ * should have been set.
+ */
+ deleting = cpumask_andnot(tmp->delmask, tmp->delmask,
+ cs->effective_xcpus);
} else if (is_partition_invalid(cs)) {
struct cgroup_subsys_state *css;
struct cpuset *child;
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index 83ef6c781af3..844efdf029cd 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -531,6 +531,21 @@ TEST_MATRIX=(
" C1-4:P1 C3-4:P2 . . T:C4-6 . . . 0 A1:5-6|A2:4 A1:P1|A2:P2 4"
" C1-4:P1 C1-2:P2 . . T:C4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
+ # The extra CPUs gained by a child partition when its parent expands the
+ # exclusive CPUs have to be taken away from the parent.
+ " C2-6:X2-5:P1 CX3-6:P1 \
+ . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P1 ."
+ " C2-6:X2-5:P1 CX3-6:P2 \
+ . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P2 3-6"
+
+ # Both expansion and contraction of parent's effective_xcpus will be
+ # correctly handled in child partition and the child can be invalidated
+ # if a populated parent could lose all its effective_cpus.
+ " C2-6:X2-5:P1 CX3,5-6:P2 \
+ . . X4-6 . . . 0 A1:4|A2:5-6|XA2:5-6 A1:P1|A2:P2 5-6"
+ " C2-6:X2-5:P1 CX3-6:P2 \
+ . . T:X4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
+
#
# old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
# ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
--
2.56.0
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH-next] cgroup/cpuset: Fix incorrect CPU accounting with parent's effective_xcpus expansion
2026-10-28 15:26 [PATCH-next] cgroup/cpuset: Fix incorrect CPU accounting with parent's effective_xcpus expansion Waiman Long
@ 2026-10-29 9:42 ` Guopeng Zhang
2026-10-29 18:04 ` Waiman Long
0 siblings, 1 reply; 3+ messages in thread
From: Guopeng Zhang @ 2026-10-29 9:42 UTC (permalink / raw)
To: Waiman Long, Ridong Chen, Tejun Heo, Johannes Weiner,
Michal Koutný, Shuah Khan
Cc: cgroups, linux-kernel, linux-kselftest
在 2026/10/28 23:26, Waiman Long 写道:
> Commit ec0254b9eb49 ("cgroup/cpuset: Release invalid isolated CPUs with
> a shrunk root partition parent") fixes incorrect isolated_cpus accounting
> when contraction of a parent's effective_xcpus can cause a child partition
> to lose isolated CPUs. Expansion of parent's effective_cpus can also allow
> a child partition to gain more effective_xcpus. However, the current code
> doesn't handle this case correctly leading to incorrect effective_cpus
> and isolated_cpus accounting. Fix that by looking for this possible
> expansion of effective_xcpus and perform the proper accounting action.
>
> New test cases are added to test this effective_xcpus expansion scenarios.
>
> Reported-by: Guopeng Zhang <guopeng.zhang@linux.dev>
> Link: https://lore.kernel.org/lkml/20261027123837.100909-1-guopeng.zhang@linux.dev
> Signed-off-by: Waiman Long <longman@redhat.com>
I have tested this patch. In the scenarios I tested, the double grant
and the isolated_cpus accounting after the expansion are now correct.
> ---
> kernel/cgroup/cpuset.c | 12 ++++++++++++
> tools/testing/selftests/cgroup/test_cpuset_prs.sh | 15 +++++++++++++++
> 2 files changed, 27 insertions(+)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 3219f927c35e..39c81a0a8ab9 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2097,6 +2097,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
> parent->effective_xcpus);
> if (!cpumask_empty(tmp->addmask))
> isolated_cpus_release(cs, tmp->addmask);
> + /* Expansion of parent's effective_xcpus is handled below */
> }
> if (nocpu) {
> part_error = PERR_NOCPUS;
> @@ -2106,11 +2107,22 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
> parent->effective_xcpus);
> } else if ((parent_prs == PRS_ISOLATED) &&
> ((old_prs == PRS_ROOT) || (old_prs == -PRS_ROOT))) {
> + /* Parent partition state changed to PRS_ISOLATED */
> part_error = PERR_ISOPARENT;
> if (old_prs == PRS_ROOT) {
> cpumask_copy(tmp->addmask, cs->effective_xcpus);
> adding = true;
> }
> + } else if (is_partition_valid(cs) &&
> + !cpumask_equal(tmp->delmask, cs->effective_xcpus)) {
The branch is also entered when the freshly computed effective xcpus
shrink, e.g. after a parent contraction. The cpumask_andnot() then
computes an empty delta and it doesn't seem to cause any harm. Do we
need to tighten the condition?
> + /*
> + * If there is an expansion of parent's effective_xcpus,
> + * we may take more xcpus from parent. The parent's
> + * effective_cpus should still have active CPUs or nocpu
> + * should have been set.
> + */
> + deleting = cpumask_andnot(tmp->delmask, tmp->delmask,
> + cs->effective_xcpus);
> } else if (is_partition_invalid(cs)) {
> struct cgroup_subsys_state *css;
> struct cpuset *child;
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index 83ef6c781af3..844efdf029cd 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -531,6 +531,21 @@ TEST_MATRIX=(
> " C1-4:P1 C3-4:P2 . . T:C4-6 . . . 0 A1:5-6|A2:4 A1:P1|A2:P2 4"
> " C1-4:P1 C1-2:P2 . . T:C4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
>
> + # The extra CPUs gained by a child partition when its parent expands the
> + # exclusive CPUs have to be taken away from the parent.
> + " C2-6:X2-5:P1 CX3-6:P1 \
> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P1 ."
> + " C2-6:X2-5:P1 CX3-6:P2 \
> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P2 3-6"
> +
> + # Both expansion and contraction of parent's effective_xcpus will be
> + # correctly handled in child partition and the child can be invalidated
> + # if a populated parent could lose all its effective_cpus.
> + " C2-6:X2-5:P1 CX3,5-6:P2 \
> + . . X4-6 . . . 0 A1:4|A2:5-6|XA2:5-6 A1:P1|A2:P2 5-6"
> + " C2-6:X2-5:P1 CX3-6:P2 \
> + . . T:X4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
> +
> #
> # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
> # ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
BTW, about the housekeeping check issue from my previous email.
I verified it with the session below on a nohz_full=8-31 boot where
CPUs 0-7 are the housekeeping CPUs:
# cat /sys/devices/system/cpu/nohz_full
8-31
# cd /sys/fs/cgroup
# echo +cpuset > cgroup.subtree_control
# mkdir -p A/B
# echo 0-7 > A/cpuset.cpus
# echo 1-7 > A/cpuset.cpus.exclusive
# echo root > A/cpuset.cpus.partition
# echo +cpuset > A/cgroup.subtree_control
# echo 0-7 > A/B/cpuset.cpus
# echo 0-7 > A/B/cpuset.cpus.exclusive
# echo isolated > A/B/cpuset.cpus.partition
# cat /sys/fs/cgroup/cpuset.cpus.isolated
1-7
# cat A/B/cpuset.cpus.exclusive.effective
1-7
# echo 0-7 > A/cpuset.cpus.exclusive
# cat A/B/cpuset.cpus.partition
isolated
# cat /sys/fs/cgroup/cpuset.cpus.isolated
0-7
B stays a valid isolated partition holding all the housekeeping CPUs
and there is no warning at all.
If the housekeeping issue is going to be addressed in this series, is
a test case like the one below worth adding?
+ # An isolated child partition cannot grow to take over the last
+ # housekeeping CPU when its parent expands the exclusive CPUs.
+ " C0-7:X1-7:P1 C0-7:X0-7:P2 . . X0-7 . . . 0 A1:0-7 A1:P1|A2:P-2 ."
Thanks,
Guopeng
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH-next] cgroup/cpuset: Fix incorrect CPU accounting with parent's effective_xcpus expansion
2026-10-29 9:42 ` Guopeng Zhang
@ 2026-10-29 18:04 ` Waiman Long
0 siblings, 0 replies; 3+ messages in thread
From: Waiman Long @ 2026-10-29 18:04 UTC (permalink / raw)
To: Guopeng Zhang, Ridong Chen, Tejun Heo, Johannes Weiner,
Michal Koutný, Shuah Khan
Cc: cgroups, linux-kernel, linux-kselftest
On 10/29/26 5:42 AM, Guopeng Zhang wrote:
>
> 在 2026/10/28 23:26, Waiman Long 写道:
>> Commit ec0254b9eb49 ("cgroup/cpuset: Release invalid isolated CPUs with
>> a shrunk root partition parent") fixes incorrect isolated_cpus accounting
>> when contraction of a parent's effective_xcpus can cause a child partition
>> to lose isolated CPUs. Expansion of parent's effective_cpus can also allow
>> a child partition to gain more effective_xcpus. However, the current code
>> doesn't handle this case correctly leading to incorrect effective_cpus
>> and isolated_cpus accounting. Fix that by looking for this possible
>> expansion of effective_xcpus and perform the proper accounting action.
>>
>> New test cases are added to test this effective_xcpus expansion scenarios.
>>
>> Reported-by: Guopeng Zhang <guopeng.zhang@linux.dev>
>> Link: https://lore.kernel.org/lkml/20261027123837.100909-1-guopeng.zhang@linux.dev
>> Signed-off-by: Waiman Long <longman@redhat.com>
> I have tested this patch. In the scenarios I tested, the double grant
> and the isolated_cpus accounting after the expansion are now correct.
>
>> ---
>> kernel/cgroup/cpuset.c | 12 ++++++++++++
>> tools/testing/selftests/cgroup/test_cpuset_prs.sh | 15 +++++++++++++++
>> 2 files changed, 27 insertions(+)
>>
>> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
>> index 3219f927c35e..39c81a0a8ab9 100644
>> --- a/kernel/cgroup/cpuset.c
>> +++ b/kernel/cgroup/cpuset.c
>> @@ -2097,6 +2097,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>> parent->effective_xcpus);
>> if (!cpumask_empty(tmp->addmask))
>> isolated_cpus_release(cs, tmp->addmask);
>> + /* Expansion of parent's effective_xcpus is handled below */
>> }
>> if (nocpu) {
>> part_error = PERR_NOCPUS;
>> @@ -2106,11 +2107,22 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd,
>> parent->effective_xcpus);
>> } else if ((parent_prs == PRS_ISOLATED) &&
>> ((old_prs == PRS_ROOT) || (old_prs == -PRS_ROOT))) {
>> + /* Parent partition state changed to PRS_ISOLATED */
>> part_error = PERR_ISOPARENT;
>> if (old_prs == PRS_ROOT) {
>> cpumask_copy(tmp->addmask, cs->effective_xcpus);
>> adding = true;
>> }
>> + } else if (is_partition_valid(cs) &&
>> + !cpumask_equal(tmp->delmask, cs->effective_xcpus)) {
> The branch is also entered when the freshly computed effective xcpus
> shrink, e.g. after a parent contraction. The cpumask_andnot() then
> computes an empty delta and it doesn't seem to cause any harm. Do we
> need to tighten the condition?
I intentionally made it simpler. For the shrink case, deleting will be
false and nothing will be done.
>
>> + /*
>> + * If there is an expansion of parent's effective_xcpus,
>> + * we may take more xcpus from parent. The parent's
>> + * effective_cpus should still have active CPUs or nocpu
>> + * should have been set.
>> + */
>> + deleting = cpumask_andnot(tmp->delmask, tmp->delmask,
>> + cs->effective_xcpus);
>> } else if (is_partition_invalid(cs)) {
>> struct cgroup_subsys_state *css;
>> struct cpuset *child;
>> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> index 83ef6c781af3..844efdf029cd 100755
>> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
>> @@ -531,6 +531,21 @@ TEST_MATRIX=(
>> " C1-4:P1 C3-4:P2 . . T:C4-6 . . . 0 A1:5-6|A2:4 A1:P1|A2:P2 4"
>> " C1-4:P1 C1-2:P2 . . T:C4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
>>
>> + # The extra CPUs gained by a child partition when its parent expands the
>> + # exclusive CPUs have to be taken away from the parent.
>> + " C2-6:X2-5:P1 CX3-6:P1 \
>> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P1 ."
>> + " C2-6:X2-5:P1 CX3-6:P2 \
>> + . . X2-6 . . . 0 A1:2|A2:3-6|XA2:3-6 A1:P1|A2:P2 3-6"
>> +
>> + # Both expansion and contraction of parent's effective_xcpus will be
>> + # correctly handled in child partition and the child can be invalidated
>> + # if a populated parent could lose all its effective_cpus.
>> + " C2-6:X2-5:P1 CX3,5-6:P2 \
>> + . . X4-6 . . . 0 A1:4|A2:5-6|XA2:5-6 A1:P1|A2:P2 5-6"
>> + " C2-6:X2-5:P1 CX3-6:P2 \
>> + . . T:X4-6 . . . 0 A1:4-6|A2:4-6 A1:P1|A2:P-2 ."
>> +
>> #
>> # old-A1 old-A2 old-A3 old-B1 new-A1 new-A2 new-A3 new-B1 fail ECPUs Pstate ISOLCPUS
>> # ------ ------ ------ ------ ------ ------ ------ ------ ---- ----- ------ --------
> BTW, about the housekeeping check issue from my previous email.
> I verified it with the session below on a nohz_full=8-31 boot where
> CPUs 0-7 are the housekeeping CPUs:
>
> # cat /sys/devices/system/cpu/nohz_full
> 8-31
> # cd /sys/fs/cgroup
> # echo +cpuset > cgroup.subtree_control
> # mkdir -p A/B
> # echo 0-7 > A/cpuset.cpus
> # echo 1-7 > A/cpuset.cpus.exclusive
> # echo root > A/cpuset.cpus.partition
> # echo +cpuset > A/cgroup.subtree_control
> # echo 0-7 > A/B/cpuset.cpus
> # echo 0-7 > A/B/cpuset.cpus.exclusive
> # echo isolated > A/B/cpuset.cpus.partition
> # cat /sys/fs/cgroup/cpuset.cpus.isolated
> 1-7
> # cat A/B/cpuset.cpus.exclusive.effective
> 1-7
> # echo 0-7 > A/cpuset.cpus.exclusive
> # cat A/B/cpuset.cpus.partition
> isolated
> # cat /sys/fs/cgroup/cpuset.cpus.isolated
> 0-7
>
> B stays a valid isolated partition holding all the housekeeping CPUs
> and there is no warning at all.
>
> If the housekeeping issue is going to be addressed in this series, is
> a test case like the one below worth adding?
>
> + # An isolated child partition cannot grow to take over the last
> + # housekeeping CPU when its parent expands the exclusive CPUs.
> + " C0-7:X1-7:P1 C0-7:X0-7:P2 . . X0-7 . . . 0 A1:0-7 A1:P1|A2:P-2 ."
>
>
I will fix that with another patch.
Cheers,
Longman
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