cgroup.c: Use built-in RCU list checking

list_for_each_entry_rcu has built-in RCU and lock checking.
Pass cond argument to list_for_each_entry_rcu() to silence
false lockdep warning when  CONFIG_PROVE_RCU_LIST is enabled
by default.

Even though the function css_next_child() already checks if
cgroup_mutex or rcu_read_lock() is held using
cgroup_assert_mutex_or_rcu_locked(), there is a need to pass
cond to list_for_each_entry_rcu() to avoid false positive
lockdep warning.

Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Acked-by: Michal Koutný <mkoutny@suse.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index b4c4c4f..7a310db 100644 (file)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4148,7 +4148,8 @@ struct cgroup_subsys_state *css_next_child(struct cgroup_subsys_state *pos,
        } else if (likely(!(pos->flags & CSS_RELEASED))) {
                next = list_entry_rcu(pos->sibling.next, struct cgroup_subsys_state, sibling);
        } else {
-               list_for_each_entry_rcu(next, &parent->children, sibling)
+               list_for_each_entry_rcu(next, &parent->children, sibling,
+                                       lockdep_is_held(&cgroup_mutex))
                        if (next->serial_nr > pos->serial_nr)
                                break;
        }