[PATCH v2 0/3] cgroup/cpuset: Preserve boot-isolated CPUs on partition release

[PATCH v2 0/3] cgroup/cpuset: Preserve boot-isolated CPUs on partition release

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

This series fixes the loss of boot-isolated CPUs when an isolated cpuset
partition is released. It also removes a selftest comparison against a
boot-only sysfs mask which cannot track dynamic cpuset isolation.

---
Changes since v1:
- split the boot-isolation fixes from the original 17-patch series;
- explain why the boot-only sysfs mask cannot validate dynamic cpuset
  isolation;
- add reproducers and observed/expected results to patches 1 and 2;
- no code changes.

Link: https://lore.kernel.org/all/20260820124202.517160-1-guopeng.zhang@linux.dev/

Guopeng Zhang (3):
  selftests/cgroup: Drop invalid boot isolation comparison
  cgroup/cpuset: Preserve boot-isolated CPUs on partition release
  selftests/cgroup: Add test for preserving boot-isolated CPUs

 kernel/cgroup/cpuset.c                        | 39 ++++++++---
 .../selftests/cgroup/test_cpuset_prs.sh       | 64 +++++++++++++++++--
 2 files changed, 87 insertions(+), 16 deletions(-)


base-commit: 6a746cd265aed59107ebdaa9ce039bb832922969
-- 
2.43.0

[PATCH v2 1/3] selftests/cgroup: Drop invalid boot isolation comparison

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

check_isolcpus() clears ISOLCPUS before rebuilding it from sched domain
data. Comparing that empty value with
/sys/devices/system/cpu/isolated makes the test fail whenever
isolcpus=domain is present.

That sysfs file is generated from HK_TYPE_DOMAIN_BOOT and does not change
when cpuset updates HK_TYPE_DOMAIN. Re-reading it cannot validate dynamic
housekeeping updates. The cpuset.cpus.isolated and sched domain checks
already cover the two dynamic interfaces, so remove the invalid comparison.

This can be reproduced on a kernel booted with isolcpus=domain,15:

    # tools/testing/selftests/cgroup/test_cpuset_prs.sh

The test fails its first state-matrix isolation check before the change and
continues past that check afterward.

Fixes: 6df415aa46ec ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index da8f7b920178..fdb3185570d4 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -797,7 +797,6 @@ check_isolcpus()
 	EXPECTED_ISOLCPUS=$1
 	ISCPUS=${CGROUP2}/cpuset.cpus.isolated
 	ISOLCPUS=$(cat $ISCPUS)
-	HKICPUS=$(cat /sys/devices/system/cpu/isolated)
 	LASTISOLCPU=
 	SCHED_DOMAINS=/sys/kernel/debug/sched/domains
 	if [[ $EXPECTED_ISOLCPUS = . ]]
@@ -835,11 +834,6 @@ check_isolcpus()
 	ISOLCPUS=
 	EXPECTED_ISOLCPUS=$EXPECTED_SDOMAIN
 
-	#
-	# The inverse of HK_TYPE_DOMAIN cpumask in $HKICPUS should match $ISOLCPUS
-	#
-	[[ "$ISOLCPUS" != "$HKICPUS" ]] && return 1
-
 	#
 	# Use the sched domain in debugfs to check isolated CPUs, if available
 	#
-- 
2.43.0

[PATCH v2 2/3] cgroup/cpuset: Preserve boot-isolated CPUs on partition release

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

isolated_cpus tracks CPUs isolated with isolcpus= as well as CPUs in
isolated cpuset partitions. When an isolated partition is released,
isolated_cpus_update() removes its whole CPU mask. This also clears CPUs
which were already isolated at boot.

This can be reproduced on a cgroup v2 system booted with
isolcpus=domain,15:

    cd /sys/fs/cgroup
    echo +cpuset > cgroup.subtree_control
    mkdir cpuset-repro
    echo 15 > cpuset-repro/cpuset.cpus
    echo isolated > cpuset-repro/cpuset.cpus.partition
    echo member > cpuset-repro/cpuset.cpus.partition
    cat cpuset.cpus.isolated

CPU 15 is absent before the change. It must remain in
cpuset.cpus.isolated after the partition is released.

Update isolated_cpus one CPU at a time and keep CPUs outside the
boot-time domain housekeeping mask isolated.

Fixes: c188f33c864e ("cgroup/cpuset: Account for boot time isolated CPUs")
Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 kernel/cgroup/cpuset.c | 39 +++++++++++++++++++++++++++++----------
 1 file changed, 29 insertions(+), 10 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index d100634fa12b..2538faac9aba 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1259,6 +1259,28 @@ static void reset_partition_data(struct cpuset *cs)
 		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
 }
 
+/* Return true if isolated_cpus changes. */
+static bool isolated_cpu_update(int new_prs, int cpu)
+{
+	lockdep_assert_held(&callback_lock);
+	lockdep_assert_held(&cpuset_mutex);
+
+	if (new_prs == PRS_ISOLATED) {
+		if (cpumask_test_cpu(cpu, isolated_cpus))
+			return false;
+		cpumask_set_cpu(cpu, isolated_cpus);
+		return true;
+	}
+
+	/* CPUs isolated at boot must remain isolated. */
+	if (!cpumask_test_cpu(cpu,
+			      housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)) ||
+	    !cpumask_test_cpu(cpu, isolated_cpus))
+		return false;
+	cpumask_clear_cpu(cpu, isolated_cpus);
+	return true;
+}
+
 /*
  * isolated_cpus_update - Update the isolated_cpus mask
  * @old_prs: old partition_root_state
@@ -1267,19 +1289,16 @@ static void reset_partition_data(struct cpuset *cs)
  */
 static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus)
 {
+	bool updated = false;
+	int cpu;
+
 	WARN_ON_ONCE(old_prs == new_prs);
 	lockdep_assert_held(&callback_lock);
 	lockdep_assert_held(&cpuset_mutex);
-	if (new_prs == PRS_ISOLATED) {
-		if (cpumask_subset(xcpus, isolated_cpus))
-			return;
-		cpumask_or(isolated_cpus, isolated_cpus, xcpus);
-	} else {
-		if (!cpumask_intersects(xcpus, isolated_cpus))
-			return;
-		cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
-	}
-	update_housekeeping = true;
+	for_each_cpu(cpu, xcpus)
+		updated |= isolated_cpu_update(new_prs, cpu);
+	if (updated)
+		update_housekeeping = true;
 }
 
 /*
-- 
2.43.0

[PATCH v2 3/3] selftests/cgroup: Add test for preserving boot-isolated CPUs

[Guopeng Zhang]

From: Guopeng Zhang <zhangguopeng@kylinos.cn>

Put a CPU isolated at boot into an isolated partition, change the
partition back to member and check that the CPU remains isolated.

Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
---
 .../selftests/cgroup/test_cpuset_prs.sh       | 58 +++++++++++++++++++
 1 file changed, 58 insertions(+)

diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index fdb3185570d4..131d8b4551ef 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -1155,6 +1155,63 @@ test_isolated()
 	pause 0.05
 }
 
+#
+# Select an online CPU isolated from scheduler domains at boot.
+# $1: test name used in the skip message
+#
+get_boot_isolated_cpu()
+{
+	TEST_NAME=$1
+	BOOT_ISOLATED_FILE=/sys/devices/system/cpu/isolated
+
+	[[ -r $BOOT_ISOLATED_FILE ]] || {
+		echo "$TEST_NAME test SKIPPED: boot isolation state unavailable"
+		return 1
+	}
+	BOOT_CPUS=$(cat $BOOT_ISOLATED_FILE)
+	[[ -n "$BOOT_CPUS" ]] || {
+		echo "$TEST_NAME test SKIPPED: no boot-isolated CPU"
+		return 1
+	}
+
+	BOOT_CPU=$(echo "$BOOT_CPUS" | sed -e 's/[,-].*//')
+	CPU_ONLINE=/sys/devices/system/cpu/cpu${BOOT_CPU}/online
+	[[ ! -e $CPU_ONLINE || $(cat $CPU_ONLINE) -eq 1 ]] || {
+		echo "$TEST_NAME test SKIPPED: CPU $BOOT_CPU is offline"
+		return 1
+	}
+}
+
+#
+# A CPU isolated at boot must stay isolated after it is released by a dynamic
+# isolated partition.
+#
+test_boot_isolated()
+{
+	TEST_NAME="Boot-isolated CPU partition release"
+	get_boot_isolated_cpu "$TEST_NAME" || return 0
+	echo "Running $TEST_NAME test ..."
+
+	cd $CGROUP2/test
+	echo member > cpuset.cpus.partition
+	echo $BOOT_CPU > cpuset.cpus
+	[[ $(cat cpuset.cpus.effective) = "$BOOT_CPU" ]] || {
+		echo "$TEST_NAME test SKIPPED: CPU $BOOT_CPU is unavailable"
+		echo "" > cpuset.cpus
+		cd $CGROUP2
+		return 0
+	}
+	test_partition isolated
+	test_partition member
+	check_isolcpus "." || {
+		echo "Boot-isolated CPU $BOOT_CPU was lost after partition release"
+		exit 1
+	}
+	echo "" > cpuset.cpus
+	cd $CGROUP2
+	echo "$TEST_NAME test PASSED."
+}
+
 #
 # Wait for inotify event for the given file and read it
 # $1: cgroup file to wait for
@@ -1226,5 +1283,6 @@ trap cleanup 0 2 3 6
 run_state_test TEST_MATRIX
 run_remote_state_test REMOTE_TEST_MATRIX
 test_isolated
+test_boot_isolated
 test_inotify
 echo "All tests PASSED."
-- 
2.43.0

Re: [PATCH v2 1/3] selftests/cgroup: Drop invalid boot isolation comparison

[Waiman Long]

On 8/23/26 10:01 PM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> check_isolcpus() clears ISOLCPUS before rebuilding it from sched domain
> data. Comparing that empty value with
> /sys/devices/system/cpu/isolated makes the test fail whenever
> isolcpus=domain is present.
>
> That sysfs file is generated from HK_TYPE_DOMAIN_BOOT and does not change
> when cpuset updates HK_TYPE_DOMAIN. Re-reading it cannot validate dynamic
> housekeeping updates. The cpuset.cpus.isolated and sched domain checks
> already cover the two dynamic interfaces, so remove the invalid comparison.
>
> This can be reproduced on a kernel booted with isolcpus=domain,15:
>
>      # tools/testing/selftests/cgroup/test_cpuset_prs.sh
>
> The test fails its first state-matrix isolation check before the change and
> continues past that check afterward.
>
> Fixes: 6df415aa46ec ("cgroup/cpuset: Defer housekeeping_update() calls from CPU hotplug to workqueue")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 6 ------
>   1 file changed, 6 deletions(-)
>
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index da8f7b920178..fdb3185570d4 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -797,7 +797,6 @@ check_isolcpus()
>   	EXPECTED_ISOLCPUS=$1
>   	ISCPUS=${CGROUP2}/cpuset.cpus.isolated
>   	ISOLCPUS=$(cat $ISCPUS)
> -	HKICPUS=$(cat /sys/devices/system/cpu/isolated)
>   	LASTISOLCPU=
>   	SCHED_DOMAINS=/sys/kernel/debug/sched/domains
>   	if [[ $EXPECTED_ISOLCPUS = . ]]
> @@ -835,11 +834,6 @@ check_isolcpus()
>   	ISOLCPUS=
>   	EXPECTED_ISOLCPUS=$EXPECTED_SDOMAIN
>   
> -	#
> -	# The inverse of HK_TYPE_DOMAIN cpumask in $HKICPUS should match $ISOLCPUS
> -	#
> -	[[ "$ISOLCPUS" != "$HKICPUS" ]] && return 1
> -
>   	#
>   	# Use the sched domain in debugfs to check isolated CPUs, if available
>   	#

The /sys/devices/system/cpu/isolated had recently be changed to report 
the boot time isolcpus=domain value. So the check is no longer valid and 
should be removed. Of course the position of the check is also 
problematic. So it should be removed.

Reviewed-by: Waiman Long <longman@redhat.com>

Re: [PATCH v2 2/3] cgroup/cpuset: Preserve boot-isolated CPUs on partition release

[Waiman Long]

On 8/23/26 10:01 PM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> isolated_cpus tracks CPUs isolated with isolcpus= as well as CPUs in
> isolated cpuset partitions. When an isolated partition is released,
> isolated_cpus_update() removes its whole CPU mask. This also clears CPUs
> which were already isolated at boot.
>
> This can be reproduced on a cgroup v2 system booted with
> isolcpus=domain,15:
>
>      cd /sys/fs/cgroup
>      echo +cpuset > cgroup.subtree_control
>      mkdir cpuset-repro
>      echo 15 > cpuset-repro/cpuset.cpus
>      echo isolated > cpuset-repro/cpuset.cpus.partition
>      echo member > cpuset-repro/cpuset.cpus.partition
>      cat cpuset.cpus.isolated
>
> CPU 15 is absent before the change. It must remain in
> cpuset.cpus.isolated after the partition is released.
>
> Update isolated_cpus one CPU at a time and keep CPUs outside the
> boot-time domain housekeeping mask isolated.
>
> Fixes: c188f33c864e ("cgroup/cpuset: Account for boot time isolated CPUs")
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   kernel/cgroup/cpuset.c | 39 +++++++++++++++++++++++++++++----------
>   1 file changed, 29 insertions(+), 10 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index d100634fa12b..2538faac9aba 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1259,6 +1259,28 @@ static void reset_partition_data(struct cpuset *cs)
>   		cpumask_copy(cs->effective_cpus, parent->effective_cpus);
>   }
>   
> +/* Return true if isolated_cpus changes. */
> +static bool isolated_cpu_update(int new_prs, int cpu)
> +{
> +	lockdep_assert_held(&callback_lock);
> +	lockdep_assert_held(&cpuset_mutex);
> +
> +	if (new_prs == PRS_ISOLATED) {
> +		if (cpumask_test_cpu(cpu, isolated_cpus))
> +			return false;
> +		cpumask_set_cpu(cpu, isolated_cpus);
> +		return true;
> +	}
> +
> +	/* CPUs isolated at boot must remain isolated. */
> +	if (!cpumask_test_cpu(cpu,
> +			      housekeeping_cpumask(HK_TYPE_DOMAIN_BOOT)) ||
> +	    !cpumask_test_cpu(cpu, isolated_cpus))
> +		return false;
> +	cpumask_clear_cpu(cpu, isolated_cpus);
> +	return true;
> +}
> +
>   /*
>    * isolated_cpus_update - Update the isolated_cpus mask
>    * @old_prs: old partition_root_state
> @@ -1267,19 +1289,16 @@ static void reset_partition_data(struct cpuset *cs)
>    */
>   static void isolated_cpus_update(int old_prs, int new_prs, struct cpumask *xcpus)
>   {
> +	bool updated = false;
> +	int cpu;
> +
>   	WARN_ON_ONCE(old_prs == new_prs);
>   	lockdep_assert_held(&callback_lock);
>   	lockdep_assert_held(&cpuset_mutex);
> -	if (new_prs == PRS_ISOLATED) {
> -		if (cpumask_subset(xcpus, isolated_cpus))
> -			return;
> -		cpumask_or(isolated_cpus, isolated_cpus, xcpus);
> -	} else {
> -		if (!cpumask_intersects(xcpus, isolated_cpus))
> -			return;
> -		cpumask_andnot(isolated_cpus, isolated_cpus, xcpus);
> -	}
> -	update_housekeeping = true;
> +	for_each_cpu(cpu, xcpus)
> +		updated |= isolated_cpu_update(new_prs, cpu);
> +	if (updated)
> +		update_housekeeping = true;
>   }
>   
>   /*

The code is technically correct. However, handling it one CPU at a time 
is less efficient from my point of view. It can be handled more 
efficiently from the cpumask level. I do notice that the new 
isolated_cpu_update() helper is being used in a later patch in your 
larger series. Maybe that is the reason why you do it this way.

I am OK with this change.

Acked-by: Waiman Long <longman@redhat.com>

Re: [PATCH v2 3/3] selftests/cgroup: Add test for preserving boot-isolated CPUs

[Waiman Long]

On 8/23/26 10:01 PM, Guopeng Zhang wrote:
> From: Guopeng Zhang <zhangguopeng@kylinos.cn>
>
> Put a CPU isolated at boot into an isolated partition, change the
> partition back to member and check that the CPU remains isolated.
>
> Signed-off-by: Guopeng Zhang <zhangguopeng@kylinos.cn>
> ---
>   .../selftests/cgroup/test_cpuset_prs.sh       | 58 +++++++++++++++++++
>   1 file changed, 58 insertions(+)
>
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index fdb3185570d4..131d8b4551ef 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -1155,6 +1155,63 @@ test_isolated()
>   	pause 0.05
>   }
>   
> +#
> +# Select an online CPU isolated from scheduler domains at boot.
> +# $1: test name used in the skip message
> +#
> +get_boot_isolated_cpu()
> +{
> +	TEST_NAME=$1
> +	BOOT_ISOLATED_FILE=/sys/devices/system/cpu/isolated
> +
> +	[[ -r $BOOT_ISOLATED_FILE ]] || {
> +		echo "$TEST_NAME test SKIPPED: boot isolation state unavailable"
> +		return 1
> +	}
> +	BOOT_CPUS=$(cat $BOOT_ISOLATED_FILE)
> +	[[ -n "$BOOT_CPUS" ]] || {
> +		echo "$TEST_NAME test SKIPPED: no boot-isolated CPU"
> +		return 1
> +	}
> +
> +	BOOT_CPU=$(echo "$BOOT_CPUS" | sed -e 's/[,-].*//')
> +	CPU_ONLINE=/sys/devices/system/cpu/cpu${BOOT_CPU}/online
> +	[[ ! -e $CPU_ONLINE || $(cat $CPU_ONLINE) -eq 1 ]] || {
> +		echo "$TEST_NAME test SKIPPED: CPU $BOOT_CPU is offline"
> +		return 1
> +	}
> +}
> +
> +#
> +# A CPU isolated at boot must stay isolated after it is released by a dynamic
> +# isolated partition.
> +#
> +test_boot_isolated()
> +{
> +	TEST_NAME="Boot-isolated CPU partition release"
> +	get_boot_isolated_cpu "$TEST_NAME" || return 0
> +	echo "Running $TEST_NAME test ..."
> +
> +	cd $CGROUP2/test
> +	echo member > cpuset.cpus.partition
> +	echo $BOOT_CPU > cpuset.cpus
> +	[[ $(cat cpuset.cpus.effective) = "$BOOT_CPU" ]] || {
> +		echo "$TEST_NAME test SKIPPED: CPU $BOOT_CPU is unavailable"
> +		echo "" > cpuset.cpus
> +		cd $CGROUP2
> +		return 0
> +	}
> +	test_partition isolated
> +	test_partition member
> +	check_isolcpus "." || {
> +		echo "Boot-isolated CPU $BOOT_CPU was lost after partition release"
> +		exit 1
> +	}
> +	echo "" > cpuset.cpus
> +	cd $CGROUP2
> +	echo "$TEST_NAME test PASSED."
> +}
> +
>   #
>   # Wait for inotify event for the given file and read it
>   # $1: cgroup file to wait for
> @@ -1226,5 +1283,6 @@ trap cleanup 0 2 3 6
>   run_state_test TEST_MATRIX
>   run_remote_state_test REMOTE_TEST_MATRIX
>   test_isolated
> +test_boot_isolated
>   test_inotify
>   echo "All tests PASSED."
Reviewed-by: Waiman Long <longman@redhat.com>

Re: [PATCH v2 0/3] cgroup/cpuset: Preserve boot-isolated CPUs on partition release

[Tejun Heo]

Hello,

On Mon, Aug 24, 2026 at 10:01:37AM +0800, Guopeng Zhang wrote:
> Guopeng Zhang (3):
>   selftests/cgroup: Drop invalid boot isolation comparison
>   cgroup/cpuset: Preserve boot-isolated CPUs on partition release
>   selftests/cgroup: Add test for preserving boot-isolated CPUs

Applied 1-3 to cgroup/for-7.3-fixes with Waiman's review tags added.

Thanks.

--
tejun