From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Date: Sat, 18 Jan 2020 03:10:51 +0000 (+0530)
Subject: cgroup.c: Use built-in RCU list checking
X-Git-Tag: v5.7-rc1~107^2~15
X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=3010c5b9f5f476b35b24955f08a3a6c06ec8e878;p=users%2Fjedix%2Flinux-maple.git

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 b4c4c4fbd6de..7a310db6c807 100644
--- 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;
 	}