[PATCH v2 1/2] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict

[PATCH v2 1/2] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable() on subpartitions_cpus conflict

[Hui Peng]

When a remote partition is created underneath an existing local partition
via a non-partition (PRS_MEMBER) intermediate cgroup, update_prstate() sees
parent->partition_root_state == PRS_MEMBER and calls
remote_partition_enable().

Commit 86888c7bd117 ("cgroup/cpuset: Add warnings to catch inconsistency
in exclusive CPUs") replaced the cpumask_intersects(tmp->new_cpus,
subpartitions_cpus) error check in remote_partition_enable() with
WARN_ON_ONCE(). As a result, remote_partition_enable() emits a warning
and proceeds to enable the remote partition on CPUs that are already
owned by the ancestor local partition in subpartitions_cpus.

This can be reproduced on Linux 7.3.0-rc3 with:

  mkdir -p /tmp/cg1
  mount -t cgroup2 none /tmp/cg1
  echo "+cpuset" > /tmp/cg1/cgroup.subtree_control

  mkdir /tmp/cg1/A
  echo 1 > /tmp/cg1/A/cpuset.cpus
  echo 1 > /tmp/cg1/A/cpuset.cpus.exclusive
  echo root > /tmp/cg1/A/cpuset.cpus.partition
  echo "+cpuset" > /tmp/cg1/A/cgroup.subtree_control

  mkdir /tmp/cg1/A/B
  echo 1 > /tmp/cg1/A/B/cpuset.cpus
  echo 1 > /tmp/cg1/A/B/cpuset.cpus.exclusive
  echo "+cpuset" > /tmp/cg1/A/B/cgroup.subtree_control

  mkdir /tmp/cg1/A/B/D
  echo 1 > /tmp/cg1/A/B/D/cpuset.cpus
  echo 1 > /tmp/cg1/A/B/D/cpuset.cpus.exclusive
  echo root > /tmp/cg1/A/B/D/cpuset.cpus.partition

which triggers:

  WARNING: kernel/cgroup/cpuset.c:1594 at remote_partition_enable+0x1c1/0x300

and leaves both /tmp/cg1/A and /tmp/cg1/A/B/D as active root partitions
claiming exclusive CPU 1.

Fix this by returning PERR_NOCPUS when tmp->new_cpus intersects
subpartitions_cpus in remote_partition_enable(), matching the error code
used by remote_cpus_update() for the same subpartitions_cpus conflict, 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 the reproducer above and
tools/testing/selftests/cgroup/test_cpuset_prs.sh.

Fixes: 86888c7bd117 ("cgroup/cpuset: Add warnings to catch inconsistency in exclusive CPUs")
Cc: stable@vger.kernel.org
Signed-off-by: Hui Peng <benquike@gmail.com>
---
Changes in v2:
- Split into a 2-patch series (1/2 for remote_partition_enable(), 2/2 for
  validate_partition() and cpus_excl_conflict()).
- Return PERR_NOCPUS instead of PERR_INVCPUS when tmp->new_cpus intersects
  subpartitions_cpus to match remote_cpus_update(), as suggested by
  Guopeng Zhang.
- Add regression test to tools/testing/selftests/cgroup/test_cpuset_prs.sh
  and include the step-by-step reproducer in the commit description as
  requested by Ridong Chen.

 kernel/cgroup/cpuset.c                        | 3 ++-
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 52eb66e3353e..7381fa8502e7 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1591,10 +1591,11 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	 * above it or remote partition root underneath it is not allowed.
 	 */
 	compute_excpus(cs, tmp->new_cpus);
-	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
 	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
 	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
 		return PERR_INVCPUS;
+	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
+		return PERR_NOCPUS;
 	if (((new_prs == PRS_ISOLATED) &&
 	     !isolated_cpus_can_update(tmp->new_cpus, NULL)) ||
 	    prstate_housekeeping_conflict(new_prs, tmp->new_cpus))
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index 3f7e81709365..b732078bf319 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -298,6 +298,8 @@ TEST_MATRIX=(
 	" 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"
+	" CX1-3:P1 CX1-3  CX1-3    .      .      .      P1     .     0 A1:1-3|A2:1-3|A3:1-3 \
+								       A1:P1|A2:P0|A3:P-1"
 
 	# Remote partition offline tests
 	"   C0-3    C1-3  C2-3     .    X2-3   X2-3 X2-3:P2:O2=0 .   0 A1:0-1|A2:1|A3:3 A1:P0|A3:P2 2-3"
-- 
2.49.0

[PATCH v2 2/2] cgroup/cpuset: prevent local partition activation over remote partition and sibling xcpus conflict

[Hui Peng]

Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
partition over a remote one") added a check in update_prstate() to reject
creating a top-level local partition whose cs->exclusive_cpus intersects
subpartitions_cpus.

However, two paths still allow overlapping exclusive CPU ownership between
a top-level local partition and a remote partition or sibling:

1. If a top-level cgroup A1 has cpuset.cpus.exclusive set, is first set to
   "root" while cpuset.cpus is empty (becoming "root invalid"), has a
   child A1/A2 enabled as a remote partition on those exclusive CPUs, and
   then receives CPUs via A1/cpuset.cpus, update_cpumasks_hier() calls
   validate_partition() without going through update_prstate(). Because
   validate_partition() does not check trialcs->exclusive_cpus against
   subpartitions_cpus, A1 transitions from "root invalid" to a valid local
   partition over the existing remote partition A1/A2 and triggers:

     WARNING: kernel/cgroup/cpuset.c:1866 at update_parent_effective_cpumask+0x54a/0x8a0

2. 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.

Fix these issues by:
- Checking trialcs->exclusive_cpus against subpartitions_cpus in
  validate_partition() when !is_partition_valid(cs).
- Falling back to sibling->effective_xcpus in cpus_excl_conflict() when
  sibling->exclusive_cpus is empty.
- Adding regression test cases for both paths 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
Cc: stable@vger.kernel.org
Signed-off-by: Hui Peng <benquike@gmail.com>
---
Changes in v2:
- Split from the remote_partition_enable() fix into patch 2/2.
- Check trialcs->exclusive_cpus (rather than effective_xcpus) in
  validate_partition() when !is_partition_valid(cs) so sibling local
  partitions with overlapping cpuset.cpus continue to share remaining
  available CPUs as expected by test_cpuset_prs.sh.
- Add regression tests to tools/testing/selftests/cgroup/test_cpuset_prs.sh.

 kernel/cgroup/cpuset.c                        | 9 ++++++++-
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 3 +++
 2 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7381fa8502e7..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)
@@ -2415,6 +2418,10 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
 	if (cpumask_empty(trialcs->effective_xcpus))
 		return PERR_INVCPUS;
 
+	if ((parent == &top_cpuset) && !is_partition_valid(cs) &&
+	    cpumask_intersects(trialcs->exclusive_cpus, subpartitions_cpus))
+		return PERR_REMOTE;
+
 	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
 					  trialcs->effective_xcpus))
 		return PERR_HKEEPING;
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index b732078bf319..f62155cf6162 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -321,6 +321,8 @@ TEST_MATRIX=(
 	" C1-3: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|B1:5-6 A1:P2|B1:P0"
 	" C0-3:P2    .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
+	" X1-3:P1 CX2-3:P2  .      .    C1-3     .      .      .     0 A1:1|A2:2-3|XA2:2-3 \
+								       A1:P-1|A2:P2 2-3"
 
 	# Local partition invalidation tests
 	" C0-3:X1-3:P2 C1-3:X2-3:P2 C2-3:X3:P2 \
@@ -443,6 +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"
-- 
2.49.0

Re: [PATCH v2 2/2] cgroup/cpuset: prevent local partition activation over remote partition and sibling xcpus conflict

[Guopeng Zhang]

在 2026/9/20 16:23, Hui Peng 写道:
> Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
> partition over a remote one") added a check in update_prstate() to reject
> creating a top-level local partition whose cs->exclusive_cpus intersects
> subpartitions_cpus.
> 
> However, two paths still allow overlapping exclusive CPU ownership between
> a top-level local partition and a remote partition or sibling:
> 
> 1. If a top-level cgroup A1 has cpuset.cpus.exclusive set, is first set to
>    "root" while cpuset.cpus is empty (becoming "root invalid"), has a
>    child A1/A2 enabled as a remote partition on those exclusive CPUs, and
>    then receives CPUs via A1/cpuset.cpus, update_cpumasks_hier() calls
>    validate_partition() without going through update_prstate(). Because
>    validate_partition() does not check trialcs->exclusive_cpus against
>    subpartitions_cpus, A1 transitions from "root invalid" to a valid local
>    partition over the existing remote partition A1/A2 and triggers:
> 
>      WARNING: kernel/cgroup/cpuset.c:1866 at update_parent_effective_cpumask+0x54a/0x8a0
> 
> 2. 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.
> 
> Fix these issues by:
> - Checking trialcs->exclusive_cpus against subpartitions_cpus in
>   validate_partition() when !is_partition_valid(cs).
> - Falling back to sibling->effective_xcpus in cpus_excl_conflict() when
>   sibling->exclusive_cpus is empty.
> - Adding regression test cases for both paths 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")

I think this patch is still missing a Fixes: tag for the
cpus_excl_conflict() change.

The validate_partition() change can be covered by 6da580ec656a.

However, the sibling CPU ownership issue fixed in cpus_excl_conflict()
was introduced by the following commit:
Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")

Thanks,
Guopeng

> Cc: stable@vger.kernel.org
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> Changes in v2:
> - Split from the remote_partition_enable() fix into patch 2/2.
> - Check trialcs->exclusive_cpus (rather than effective_xcpus) in
>   validate_partition() when !is_partition_valid(cs) so sibling local
>   partitions with overlapping cpuset.cpus continue to share remaining
>   available CPUs as expected by test_cpuset_prs.sh.
> - Add regression tests to tools/testing/selftests/cgroup/test_cpuset_prs.sh.
> 
>  kernel/cgroup/cpuset.c                        | 9 ++++++++-
>  tools/testing/selftests/cgroup/test_cpuset_prs.sh | 3 +++
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 7381fa8502e7..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)
> @@ -2415,6 +2418,10 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
>  	if (cpumask_empty(trialcs->effective_xcpus))
>  		return PERR_INVCPUS;
>  
> +	if ((parent == &top_cpuset) && !is_partition_valid(cs) &&
> +	    cpumask_intersects(trialcs->exclusive_cpus, subpartitions_cpus))
> +		return PERR_REMOTE;
> +
>  	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
>  					  trialcs->effective_xcpus))
>  		return PERR_HKEEPING;
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index b732078bf319..f62155cf6162 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -321,6 +321,8 @@ TEST_MATRIX=(
>  	" C1-3: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|B1:5-6 A1:P2|B1:P0"
>  	" C0-3:P2    .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
> +	" X1-3:P1 CX2-3:P2  .      .    C1-3     .      .      .     0 A1:1|A2:2-3|XA2:2-3 \
> +								       A1:P-1|A2:P2 2-3"
>  
>  	# Local partition invalidation tests
>  	" C0-3:X1-3:P2 C1-3:X2-3:P2 C2-3:X3:P2 \
> @@ -443,6 +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"

Re: [PATCH v2 2/2] cgroup/cpuset: prevent local partition activation over remote partition and sibling xcpus conflict

[Hui Peng]

On Sun, Sep 20, 2026 at 04:57:39PM +0800, Guopeng Zhang wrote:
> I think this patch is still missing a Fixes: tag for the
> cpus_excl_conflict() change.
>
> The validate_partition() change can be covered by 6da580ec656a.
>
> However, the sibling CPU ownership issue fixed in cpus_excl_conflict()
> was introduced by the following commit:
> Fixes: 2a3602030d80 ("cgroup/cpuset: Don't invalidate sibling partitions on cpuset.cpus conflict")

Thanks for pointing this out, Guopeng!

In v3, I have split the validate_partition() change (with
Fixes: 6da580ec656a) and the cpus_excl_conflict() change (with
Fixes: 2a3602030d80) into separate patches ([PATCH v3 2/3] and
[PATCH v3 3/3]) so that each patch fixes a single logical issue with its
corresponding Fixes: tag.

Best regards,
Hui

[PATCH v3 1/3] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable()

[Hui Peng]

Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
partition over a remote one") updated update_prstate() to prevent creating
a top-level local partition whose exclusive CPUs conflict with an existing
remote partition.

However, if a top-level local partition A1 is created on CPUs 1-3, has a
non-partition member child A1/A2 with cpuset.cpus.exclusive = 1-3, and a
grandchild A1/A2/A3 is then enabled as a partition root on 1-3,
update_prstate() sees !is_partition_valid(parent) (since A1/A2 is a member)
and calls remote_partition_enable(). Because remote_partition_enable() does
not check whether tmp->new_cpus intersects subpartitions_cpus, A1/A2/A3 is
enabled as a remote partition on CPUs already owned by A1, triggering:

  WARNING: kernel/cgroup/cpuset.c:1594 at update_prstate+0xbef/0xd70

Return PERR_NOCPUS in remote_partition_enable() when tmp->new_cpus
intersects subpartitions_cpus, matching the error code used by
remote_cpus_update() for subpartitions_cpus conflicts, and add a
corresponding 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
Suggested-by: Guopeng Zhang <guopeng.zhang@linux.dev>
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
Changes in v3:
- Split the series into 3 patches (one per logical change and Fixes: tag).

 kernel/cgroup/cpuset.c                        | 4 +++-
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index c8ab89cfbe3d..7381fa8502e7 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1678,8 +1678,10 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	 * Callers must have validated that effective_xcpus is not empty.
 	 */
 	spin_lock_irq(&callback_lock);
-	if (cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
+	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus) ||
+	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
 		spin_unlock_irq(&callback_lock);
+		if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
+			return PERR_NOCPUS;
 		return PERR_HKEEPING;
 	}
 
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index a1f42ef64bc1..b732078bf319 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -298,6 +298,8 @@ TEST_MATRIX=(
 	" 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"
+	" CX1-3:P1 CX1-3  CX1-3    .      .      .      P1     .     0 A1:1-3|A2:1-3|A3:1-3 \
+								       A1:P1|A2:P0|A3:P-1"
 
 	# Remote partition offline tests
 	"   C0-3    C1-3  C2-3     .    X2-3   X2-3 X2-3:P2:O2=0 .   0 A1:0-1|A2:1|A3:3 A1:P0|A3:P2 2-3"
-- 
2.49.0

[PATCH v3 2/3] cgroup/cpuset: prevent activating local partition over remote one

[Hui Peng]

Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
partition over a remote one") added a check in update_prstate() to reject
creating a top-level local partition whose cs->exclusive_cpus intersects
subpartitions_cpus.

However, if a top-level cgroup A1 is first set to "root" with all CPUs
(CX0-7:P1, becoming "root invalid" because no CPUs would remain in
top_cpuset), has a child A1/A2 enabled as a remote partition on a subset
of those exclusive CPUs (CX2-3:P2), and A1 is then updated to a valid CPU
subset (CX1-3), update_exclusive_cpumask() / update_cpumask() calls
validate_partition() without going through update_prstate(). Because
validate_partition() does not check trialcs->exclusive_cpus against
subpartitions_cpus, A1 transitions from "root invalid" to a valid local
partition over the existing remote partition A1/A2 and triggers:

  WARNING: kernel/cgroup/cpuset.c:1943 at update_parent_effective_cpumask+0x189b/0x1fd0

Check trialcs->exclusive_cpus against subpartitions_cpus in
validate_partition() when !is_partition_valid(cs), 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
Cc: stable@vger.kernel.org
Assisted-by: LLM
Signed-off-by: Hui Peng <benquike@gmail.com>
---
Changes in v3:
- Split the validate_partition() fix (Fixes: 6da580ec656a) and the
  cpus_excl_conflict() fix (Fixes: 2a3602030d80) into separate patches.

 kernel/cgroup/cpuset.c                        | 4 ++++
 tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
 2 files changed, 6 insertions(+)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 7381fa8502e7..7c5b4a8f1f3a 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2415,6 +2415,10 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
 	if (cpumask_empty(trialcs->effective_xcpus))
 		return PERR_INVCPUS;
 
+	if ((parent == &top_cpuset) && !is_partition_valid(cs) &&
+	    cpumask_intersects(trialcs->exclusive_cpus, subpartitions_cpus))
+		return PERR_REMOTE;
+
 	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
 					  trialcs->effective_xcpus))
 		return PERR_HKEEPING;
diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
index b732078bf319..f4d1822d4e21 100755
--- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
+++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
@@ -321,6 +321,8 @@ TEST_MATRIX=(
 	" C1-3: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|B1:5-6 A1:P2|B1:P0"
 	" C0-3:P2    .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
+	" CX0-7:P1 CX2-3:P2 .      .    CX1-3    .      .      .     0 A1:1|A2:2-3|XA2:2-3 \
+								       A1:P-1|A2:P2 2-3"
 
 	# Local partition invalidation tests
 	" C0-3:X1-3:P2 C1-3:X2-3:P2 C2-3:X3:P2 \
-- 
2.49.0

[PATCH v3 3/3] cgroup/cpuset: check sibling effective_xcpus in cpus_excl_conflict()

[Hui Peng]

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>
---
Changes in v3:
- Split out from the validate_partition() fix into patch 3/3 and add the
  Fixes tag for commit 2a3602030d80, as pointed out by Guopeng Zhang.

 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"
-- 
2.49.0

Re: [PATCH v3 1/3] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable()

[Ridong Chen]

On 9/21/2026 2:14 AM, Hui Peng wrote:
> Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
> partition over a remote one") updated update_prstate() to prevent creating
> a top-level local partition whose exclusive CPUs conflict with an existing
> remote partition.
> 
> However, if a top-level local partition A1 is created on CPUs 1-3, has a
> non-partition member child A1/A2 with cpuset.cpus.exclusive = 1-3, and a
> grandchild A1/A2/A3 is then enabled as a partition root on 1-3,
> update_prstate() sees !is_partition_valid(parent) (since A1/A2 is a member)
> and calls remote_partition_enable(). Because remote_partition_enable() does
> not check whether tmp->new_cpus intersects subpartitions_cpus, A1/A2/A3 is
> enabled as a remote partition on CPUs already owned by A1, triggering:
> 
>    WARNING: kernel/cgroup/cpuset.c:1594 at update_prstate+0xbef/0xd70
> 
> Return PERR_NOCPUS in remote_partition_enable() when tmp->new_cpus
> intersects subpartitions_cpus, matching the error code used by
> remote_cpus_update() for subpartitions_cpus conflicts, and add a
> corresponding 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
> Suggested-by: Guopeng Zhang <guopeng.zhang@linux.dev>
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> Changes in v3:
> - Split the series into 3 patches (one per logical change and Fixes: tag).
> 

What is going on here?

Please do not reply with a new series. And I think the changes should be listed 
in the cover letter. Otherwise, it will get very confusing.


>   kernel/cgroup/cpuset.c                        | 4 +++-
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
>   2 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index c8ab89cfbe3d..7381fa8502e7 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -1678,8 +1678,10 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	 * Callers must have validated that effective_xcpus is not empty.
>   	 */
>   	spin_lock_irq(&callback_lock);
> -	if (cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
> +	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus) ||
> +	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus)) {
>   		spin_unlock_irq(&callback_lock);
> +		if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
> +			return PERR_NOCPUS;
>   		return PERR_HKEEPING;
>   	}
>   

I cannot apply this patch. It seems quite different from v2.

> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index a1f42ef64bc1..b732078bf319 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -298,6 +298,8 @@ TEST_MATRIX=(
>   	" 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"
> +	" CX1-3:P1 CX1-3  CX1-3    .      .      .      P1     .     0 A1:1-3|A2:1-3|A3:1-3 \
> +								       A1:P1|A2:P0|A3:P-1"
>   
>   	# Remote partition offline tests
>   	"   C0-3    C1-3  C2-3     .    X2-3   X2-3 X2-3:P2:O2=0 .   0 A1:0-1|A2:1|A3:3 A1:P0|A3:P2 2-3"

-- 
Best regards
Ridong

Re: [PATCH v3 1/3] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable()

[Hui Peng]

On Mon, Sep 21, 2026 at 03:08:55PM +0800, Ridong Chen wrote:
> What is going on here?
>
> Please do not reply with a new series. And I think the changes should be listed
> in the cover letter. Otherwise, it will get very confusing.
>
> ...
>
> I cannot apply this patch. It seems quite different from v2.

Hi Ridong,

Sorry for the confusion and the noise. Two mistakes happened when I
prepared v3 after splitting patch 2/2 per Guopeng's feedback:

1. I mistakenly passed --in-reply-to pointing to the v2 thread and
   omitted the 0/3 cover letter.
2. Patch 1/3 was accidentally overwritten with a broken diff instead of
   the remote_partition_enable() hunk from v2 1/2:

@@ -1591,10 +1591,11 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
 	 * above it or remote partition root underneath it is not allowed.
 	 */
 	compute_excpus(cs, tmp->new_cpus);
-	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
 	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
 	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
 		return PERR_INVCPUS;
+	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
+		return PERR_NOCPUS;

Would it be OK if I post a clean, standalone [PATCH v4 0/3..3/3] series
(as a new thread with a 0/3 cover letter listing the changelog and with
the v2 1/2 diff restored in patch 1/3)?

Best regards,
Hui

Re: [PATCH v3 1/3] cgroup/cpuset: return PERR_NOCPUS in remote_partition_enable()

[Waiman Long]

On 9/22/26 4:00 AM, Hui Peng wrote:
> On Mon, Sep 21, 2026 at 03:08:55PM +0800, Ridong Chen wrote:
>> What is going on here?
>>
>> Please do not reply with a new series. And I think the changes should be listed
>> in the cover letter. Otherwise, it will get very confusing.
>>
>> ...
>>
>> I cannot apply this patch. It seems quite different from v2.
> Hi Ridong,
>
> Sorry for the confusion and the noise. Two mistakes happened when I
> prepared v3 after splitting patch 2/2 per Guopeng's feedback:
>
> 1. I mistakenly passed --in-reply-to pointing to the v2 thread and
>     omitted the 0/3 cover letter.
> 2. Patch 1/3 was accidentally overwritten with a broken diff instead of
>     the remote_partition_enable() hunk from v2 1/2:
>
> @@ -1591,10 +1591,11 @@ static int remote_partition_enable(struct cpuset *cs, int new_prs,
>   	 * above it or remote partition root underneath it is not allowed.
>   	 */
>   	compute_excpus(cs, tmp->new_cpus);
> -	WARN_ON_ONCE(cpumask_intersects(tmp->new_cpus, subpartitions_cpus));
>   	if (!cpumask_intersects(tmp->new_cpus, cpu_active_mask) ||
>   	    cpumask_subset(top_cpuset.effective_cpus, tmp->new_cpus))
>   		return PERR_INVCPUS;
> +	if (cpumask_intersects(tmp->new_cpus, subpartitions_cpus))
> +		return PERR_NOCPUS;
>
> Would it be OK if I post a clean, standalone [PATCH v4 0/3..3/3] series
> (as a new thread with a 0/3 cover letter listing the changelog and with
> the v2 1/2 diff restored in patch 1/3)?

That diff looks more correct. Please send out a new standalone v4 patch 
series with your patches.

Cheers,
Longman

> Best regards,
> Hui
>

Re: [PATCH v3 2/3] cgroup/cpuset: prevent activating local partition over remote one

[Waiman Long]

On 9/20/26 2:14 PM, Hui Peng wrote:
> Commit 6da580ec656a ("cgroup/cpuset: Don't allow creation of local
> partition over a remote one") added a check in update_prstate() to reject
> creating a top-level local partition whose cs->exclusive_cpus intersects
> subpartitions_cpus.
>
> However, if a top-level cgroup A1 is first set to "root" with all CPUs
> (CX0-7:P1, becoming "root invalid" because no CPUs would remain in
> top_cpuset), has a child A1/A2 enabled as a remote partition on a subset
> of those exclusive CPUs (CX2-3:P2), and A1 is then updated to a valid CPU
> subset (CX1-3), update_exclusive_cpumask() / update_cpumask() calls
> validate_partition() without going through update_prstate(). Because
> validate_partition() does not check trialcs->exclusive_cpus against
> subpartitions_cpus, A1 transitions from "root invalid" to a valid local
> partition over the existing remote partition A1/A2 and triggers:
>
>    WARNING: kernel/cgroup/cpuset.c:1943 at update_parent_effective_cpumask+0x189b/0x1fd0
>
> Check trialcs->exclusive_cpus against subpartitions_cpus in
> validate_partition() when !is_partition_valid(cs), 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: 6da580ec656a ("cgroup/cpuset: Don't allow creation of local partition over a remote one")
> Cc: stable@vger.kernel.org
> Assisted-by: LLM
> Signed-off-by: Hui Peng <benquike@gmail.com>
> ---
> Changes in v3:
> - Split the validate_partition() fix (Fixes: 6da580ec656a) and the
>    cpus_excl_conflict() fix (Fixes: 2a3602030d80) into separate patches.
>
>   kernel/cgroup/cpuset.c                        | 4 ++++
>   tools/testing/selftests/cgroup/test_cpuset_prs.sh | 2 ++
>   2 files changed, 6 insertions(+)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 7381fa8502e7..7c5b4a8f1f3a 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -2415,6 +2415,10 @@ static enum prs_errcode validate_partition(struct cpuset *cs, struct cpuset *tri
>   	if (cpumask_empty(trialcs->effective_xcpus))
>   		return PERR_INVCPUS;
>   
> +	if ((parent == &top_cpuset) && !is_partition_valid(cs) &&
> +	    cpumask_intersects(trialcs->exclusive_cpus, subpartitions_cpus))
> +		return PERR_REMOTE;
> +
This additional check looks good.
>   	if (prstate_housekeeping_conflict(trialcs->partition_root_state,
>   					  trialcs->effective_xcpus))
>   		return PERR_HKEEPING;
> diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> index b732078bf319..f4d1822d4e21 100755
> --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh
> @@ -321,6 +321,8 @@ TEST_MATRIX=(
>   	" C1-3: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|B1:5-6 A1:P2|B1:P0"
>   	" C0-3:P2    .      .    C4-6 C0-4:C0-3  .      .      .     0 A1:0-3|B1:4-6 A1:P2|B1:P0 0-3"
> +	" CX0-7:P1 CX2-3:P2 .      .    CX1-3    .      .      .     0 A1:1|A2:2-3|XA2:2-3 \
> +								       A1:P-1|A2:P2 2-3"

This test will not work because you are assuming the test system only 
have 8 CPUs. That may not be the case and 2 local partitions may be 
created instead.

Cheers,
Longman

>   
>   	# Local partition invalidation tests
>   	" C0-3:X1-3:P2 C1-3:X2-3:P2 C2-3:X3:P2 \