On Wed, Feb 02, 2022 at 10:31:03PM -0500 Waiman Long wrote:
> 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
>
This looks good. Thanks Waiman.
Tested-by: Phil Auld <pauld@xxxxxxxxxx>
Reviewed-by: Phil Auld <pauld@xxxxxxxxxx>
Cheers,
Phil
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