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cgroup/cpuset: Fix "suspicious RCU usage" lockdep warning

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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: 4716909cc5 ("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>
This commit is contained in:
Waiman Long 2022-02-02 22:31:03 -05:00 committed by Tejun Heo
parent 24f6008564
commit 2bdfd2825c
1 changed files with 10 additions and 0 deletions
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10
kernel/cgroup/cpuset.c
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@ -1550,10 +1550,15 @@ 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) {
@ -1561,8 +1566,13 @@ 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();
}