On 9/24/26 12:27 AM, Hui Peng wrote:
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"
Technically, this commit isn't wrong as it does not expect that a
remote partition can be created under a local partition. I will put the
commit to be fixed as 181c8e091aae ("cgroup/cpuset: Introduce remote
partition").
Other than that, it looks good to me.
Reviewed-by: Waiman Long <[email protected]>
Suggested-by: Guopeng Zhang <[email protected]>
Cc: [email protected]
Assisted-by: LLM
Signed-off-by: Hui Peng <[email protected]>
---
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 2538faac9aba..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"
