linux-kernel - [PATCH] cgroup.c: Use built-in RCU list checking

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Message-Id: <20200118031051.28776-1-madhuparnabhowmik10@gmail.com>
Date:   Sat, 18 Jan 2020 08:40:51 +0530
From:   madhuparnabhowmik10@...il.com
To:     tj@...nel.org, lizefan@...wei.com
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        joel@...lfernandes.org, rcu@...r.kernel.org, frextrite@...il.com,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>
Subject: [PATCH] cgroup.c: Use built-in RCU list checking

From: Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>

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@...il.com>
---
 kernel/cgroup/cgroup.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 735af8f15f95..c2959764ad95 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4152,7 +4152,8 @@ 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;
 	}
-- 
2.17.1