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* [PATCH] cgroup/cpuset: Remove redundant cpu/node masks setup in cpuset_init_smp()
@ 2022-04-25  2:09 Waiman Long
  2022-04-25  7:30 ` Feng Tang
  2022-05-13  6:33 ` [cgroup/cpuset] 7aaa45f837: kbuild.buildtime_per_iteration 2583.0% regression kernel test robot
  0 siblings, 2 replies; 5+ messages in thread
From: Waiman Long @ 2022-04-25  2:09 UTC (permalink / raw)
  To: Tejun Heo, Zefan Li, Johannes Weiner
  Cc: cgroups, linux-mm, linux-kernel, Feng Tang, Andrew Morton,
	Michal Hocko, Dave Hansen, ying.huang, Waiman Long, stable

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@vger.kernel.org
Signed-off-by: Waiman Long <longman@redhat.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


^ permalink raw reply related	[flat|nested] 5+ messages in thread

end of thread, other threads:[~2022-05-16  3:03 UTC | newest]

Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2022-04-25  2:09 [PATCH] cgroup/cpuset: Remove redundant cpu/node masks setup in cpuset_init_smp() Waiman Long
2022-04-25  7:30 ` Feng Tang
2022-04-25 14:43   ` Waiman Long
2022-05-13  6:33 ` [cgroup/cpuset] 7aaa45f837: kbuild.buildtime_per_iteration 2583.0% regression kernel test robot
2022-05-16  3:02   ` Waiman Long

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