[PATCH v2] cgroup/cpuset: Remove cpus_allowed/mems_allowed setup in cpuset_init_smp()

From: Waiman Long
Date: Mon Apr 25 2022 - 11:55:34 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.

For systems with cgroup v2 setup, cpuset_bind() is called once. For
systems with cgroup v1 setup, cpuset_bind() is called twice. It is
first called before cpuset_init_smp() in cgroup v2 mode. Then it is
called again when cgroup v1 filesystem is mounted in v1 mode after

[ 2.609781] cpuset_bind() called - v2 = 1
[ 3.079473] cpuset_init_smp() called
[ 7.103710] cpuset_bind() called - v2 = 0

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.

smp_init() is called after the first two init functions. So we don't
have a complete list of active cpus and memory nodes until later in
cpuset_init_smp() which is the right time to set up effective_cpus
and effective_mems.

To fix this problem, the potentially incorrect cpus_allowed &
mems_allowed setup in cpuset_init_smp() are removed. For cgroup v2
systems, the initial cpuset_bind() call will set them up correctly.
For cgroup v1 systems, the second call to cpuset_bind() will do the
right setup.

cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
kernel/cgroup/cpuset.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 9390bfd9f1cd..6bd8f5ef40fe 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -3390,8 +3390,9 @@ 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];
+ /*
+ * cpus_allowd/mems_allowed will be properly set up in cpuset_bind().
+ */
top_cpuset.old_mems_allowed = top_cpuset.mems_allowed;

cpumask_copy(top_cpuset.effective_cpus, cpu_active_mask);