[PATCH 5.10 73/74] cgroup/cpuset: Fix "suspicious RCU usage" lockdep warning

Greg Kroah-Hartman
2022-02-07T11:39:41Z

From: Waiman Long <longman@redhat.com>

commit 2bdfd2825c9662463371e6691b1a794e97fa36b4 upstream.

It was found that a "suspicious RCU usage" lockdep warning was issued
with the rcu_read_lock() call in update_sibling_cpumasks(). It is
because the update_cpumasks_hier() function may sleep. So we have
to release the RCU lock, call update_cpumasks_hier() and reacquire
it afterward.

Also add a percpu_rwsem_assert_held() in update_sibling_cpumasks()
instead of stating that in the comment.

Fixes: 4716909cc5c5 ("cpuset: Track cpusets that use parent's effective_cpus")
Signed-off-by: Waiman Long <longman@redhat.com>
Tested-by: Phil Auld <pauld@redhat.com>
Reviewed-by: Phil Auld <pauld@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
kernel/cgroup/cpuset.c | 10 ++++++++++
1 file changed, 10 insertions(+)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1481,10 +1481,15 @@ static void update_sibling_cpumasks(stru
struct cpuset *sibling;
struct cgroup_subsys_state *pos_css;

+ percpu_rwsem_assert_held(&cpuset_rwsem);
+
/*
* Check all its siblings and call update_cpumasks_hier()
* if their use_parent_ecpus flag is set in order for them
* to use the right effective_cpus value.
+ *
+ * The update_cpumasks_hier() function may sleep. So we have to
+ * release the RCU read lock before calling it.
*/
rcu_read_lock();
cpuset_for_each_child(sibling, pos_css, parent) {
@@ -1492,8 +1497,13 @@ static void update_sibling_cpumasks(stru
continue;
if (!sibling->use_parent_ecpus)
continue;
+ if (!css_tryget_online(&sibling->css))
+ continue;

+ rcu_read_unlock();
update_cpumasks_hier(sibling, tmp);
+ rcu_read_lock();
+ css_put(&sibling->css);
}
rcu_read_unlock();
}