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@xxxxxxxxxx>
---
kernel/cgroup/cpuset.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index dc653ab26e50..b147acece984 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1522,10 +1522,15 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
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) {
@@ -1533,8 +1538,13 @@ static void update_sibling_cpumasks(struct cpuset *parent, struct cpuset *cs,
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();
}
--
2.27.0
