[PATCH] cgroup/cpuset: Remove redundant cpu/node masks setup in cpuset_init_smp()

From: Waiman Long
Date: Sun Apr 24 2022 - 22:10:29 EST

There are 3 places where the cpu and node masks of the top cpuset can
be initialized in the order they are executed:
1) start_kernel -> cpuset_init()
2) start_kernel -> cgroup_init() -> cpuset_bind()
3) kernel_init_freeable() -> do_basic_setup() -> cpuset_init_smp()

The first cpuset_init() function just sets all the bits in the masks.
The last one executed is cpuset_init_smp() which sets up cpu and node
masks suitable for v1, but not v2. cpuset_bind() does the right setup
for both v1 and v2 assuming that effective_mems and effective_cpus have
been set up properly which is not strictly the case here. As a result,
cpu and memory node hot add may fail to update the cpu and node masks
of the top cpuset to include the newly added cpu or node in a cgroup
v2 environment.

To fix this problem, the redundant cpus_allowed and mems_allowed
mask setup in cpuset_init_smp() are removed. The effective_cpus and
effective_mems setup there are moved to cpuset_bind().

cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
kernel/cgroup/cpuset.c | 10 +++-------
1 file changed, 3 insertions(+), 7 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 9390bfd9f1cd..a2e15a43397e 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2961,6 +2961,9 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)

+ cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
+ top_cpuset.effective_mems = node_states[N_MEMORY];
if (is_in_v2_mode()) {
cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
top_cpuset.mems_allowed = node_possible_map;
@@ -3390,13 +3393,6 @@ static struct notifier_block cpuset_track_online_nodes_nb = {
void __init cpuset_init_smp(void)
- cpumask_copy(top_cpuset.cpus_allowed, cpu_active_mask);
- top_cpuset.mems_allowed = node_states[N_MEMORY];
- top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;
- cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);
- top_cpuset.effective_mems = node_states[N_MEMORY];

cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);