6.16-stable review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
[ Upstream commit 150e298ae0ccbecff2357a72fbabd80f8849ea6e ]
It was found during testing that an invalid leaf partition with an empty effective exclusive CPU list can become a valid empty partition with no CPU afer an offline/online operation of an unrelated CPU. An empty partition root is allowed in the special case that it has no task in its cgroup and has distributed out all its CPUs to its child partitions. That is certainly not the case here.
The problem is in the cpumask_subsets() test in the hotplug case (update with no new mask) of update_parent_effective_cpumask() as it also returns true if the effective exclusive CPU list is empty. Fix that by addding the cpumask_empty() test to root out this exception case. Also add the cpumask_empty() test in cpuset_hotplug_update_tasks() to avoid calling update_parent_effective_cpumask() for this special case.
Fixes: 0c7f293efc87 ("cgroup/cpuset: Add cpuset.cpus.exclusive.effective for v2") Signed-off-by: Waiman Long longman@redhat.com Signed-off-by: Tejun Heo tj@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/cgroup/cpuset.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c index 77396bab071a..f9d7799c5c94 100644 --- a/kernel/cgroup/cpuset.c +++ b/kernel/cgroup/cpuset.c @@ -1843,7 +1843,7 @@ static int update_parent_effective_cpumask(struct cpuset *cs, int cmd, if (is_partition_valid(cs)) adding = cpumask_and(tmp->addmask, xcpus, parent->effective_xcpus); - } else if (is_partition_invalid(cs) && + } else if (is_partition_invalid(cs) && !cpumask_empty(xcpus) && cpumask_subset(xcpus, parent->effective_xcpus)) { struct cgroup_subsys_state *css; struct cpuset *child; @@ -3870,9 +3870,10 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs, struct tmpmasks *tmp) partcmd = partcmd_invalidate; /* * On the other hand, an invalid partition root may be transitioned - * back to a regular one. + * back to a regular one with a non-empty effective xcpus. */ - else if (is_partition_valid(parent) && is_partition_invalid(cs)) + else if (is_partition_valid(parent) && is_partition_invalid(cs) && + !cpumask_empty(cs->effective_xcpus)) partcmd = partcmd_update;
if (partcmd >= 0) {