linux-kernel - [PATCH] cgroup/cpuset: Remove redundant cpu/node masks setup in cpuset_init

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Date:   Sun, 24 Apr 2022 22:09:26 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>
Cc:     cgroups@...r.kernel.org, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Feng Tang <feng.tang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>, ying.huang@...el.com,
        Waiman Long <longman@...hat.com>, stable@...r.kernel.org
Subject: [PATCH] cgroup/cpuset: Remove redundant cpu/node masks setup in cpuset_init_smp()

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@...r.kernel.org
Signed-off-by: Waiman Long <longman@...hat.com>
---
 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)
 	percpu_down_write(&cpuset_rwsem);
 	spin_lock_irq(&callback_lock);
 
+	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];
-
 	register_hotmemory_notifier(&cpuset_track_online_nodes_nb);
 
 	cpuset_migrate_mm_wq = alloc_ordered_workqueue("cpuset_migrate_mm", 0);
-- 
2.27.0