On 10/20/26 9:33 AM, Guopeng Zhang wrote:
From: Guopeng Zhang <[email protected]>An invalid local partition can become valid again even when its exclusive CPUs are no longer available from its parent. This can be reproduced on a cgroup v2 system with CPUs 0-7 online: cd /sys/fs/cgroup echo +cpuset > cgroup.subtree_control mkdir A echo 1-4 > A/cpuset.cpus echo 1-4 > A/cpuset.cpus.exclusive echo root > A/cpuset.cpus.partition echo +cpuset > A/cgroup.subtree_control mkdir A/B echo 3-4 > A/B/cpuset.cpus echo 3-4 > A/B/cpuset.cpus.exclusive echo root > A/B/cpuset.cpus.partition echo 1-2 > A/cpuset.cpus.exclusive cat A/B/cpuset.cpus.partition root cat A/B/cpuset.cpus.exclusive.effective cat A/cpuset.cpus.effective 1-2 cat A/B/cpuset.cpus.effective 1-2 B is changed back to a valid root even though its exclusive CPUs are no longer available and cpuset.cpus.exclusive.effective is empty. B should remain invalid until A can provide its exclusive CPUs again. Shrinking A's exclusive CPUs invalidates B in compute_partition_effective_cpumask(). The subsequent walk in update_cpumasks_hier() tries to recover B, but update_parent_effective_cpumask() skips the recovery checks when xcpus is not a subset of parent->effective_xcpus. Since part_error is still zero, B is changed back to a valid partition. Set PERR_INVCPUS when the subset check fails so that the partition stays invalid. New test cases are added to test_cpuset_prs.sh for removing and restoring the parent's exclusive CPUs. Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2") Signed-off-by: Guopeng Zhang <[email protected]> --- kernel/cgroup/cpuset.c | 8 ++++++-- tools/testing/selftests/cgroup/test_cpuset_prs.sh | 4 ++++ 2 files changed, 10 insertions(+), 2 deletions(-) diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 585a982249ad..be80763953ed 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1986,12 +1986,16 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, cpumask_copy(tmp->addmask, cs->effective_xcpus); adding = true; } - } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) && - cpumask_subset(xcpus, parent->effective_xcpus)) { + } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus)) { struct cgroup_subsys_state *css; struct cpuset *child; bool exclusive = true;+ if (!cpumask_subset(xcpus, parent->effective_xcpus)) {+ part_error = PERR_INVCPUS; + goto write_error; + } + /* * Convert invalid partition to valid has to pass the * cpu exclusivity test as well as the housekeeping diff --git a/tools/testing/selftests/cgroup/test_cpuset_prs.sh b/tools/testing/selftests/cgroup/test_cpuset_prs.sh index d04aad697b96..f1d517647ade 100755 --- a/tools/testing/selftests/cgroup/test_cpuset_prs.sh +++ b/tools/testing/selftests/cgroup/test_cpuset_prs.sh @@ -427,6 +427,10 @@ TEST_MATRIX=( # cpuset.cpus is allowed, but those extra CPUs are ignored. " C2-3:P1 C3:P1 . . . C2-4 . . 0 A1:|A2:2-3 A1:P1|A2:P1"+ # A child cannot recover until its exclusive CPUs are available again.+ " CX1-4:P1 CX3-4:P1 . . X1-2 . . . 0 A1:1-2|A2:1-2|XA2: A1:P1|A2:P-1" + " CX1-4:P1 CX3-4:P1 . . X1-2:X1-4 . . . 0 A1:1-2|A2:3-4|XA2:3-4 A1:P1|A2:P1" + # Taking away all CPUs from parent or itself if there are tasks # will make the partition invalid. " C2-3:P1 C3:P1 . . T C2-3 . . 0 A1:2-3|A2:2-3 A1:P1|A2:P-1"
Patch 2 of my series should fix this problem too. I do borrow your test cases in my patch. I hope you don't mind about it.
Cheers, Longman
