netdev - [PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each

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Date:   Sat, 22 Feb 2020 12:08:36 +0530
From:   Amol Grover <frextrite@...il.com>
To:     "David S . Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kernel-mentees@...ts.linuxfoundation.org,
        Joel Fernandes <joel@...lfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik10@...il.com>,
        "Paul E . McKenney" <paulmck@...nel.org>,
        Amol Grover <frextrite@...il.com>
Subject: [PATCH 2/2] ipmr: Add lockdep expression to ipmr_for_each_table macro

ipmr_for_each_table() uses list_for_each_entry_rcu() for
traversing outside of an RCU read-side critical section but
under the protection of pernet_ops_rwsem. Hence add the
corresponding lockdep expression to silence the following
false-positive warning at boot:

[    0.645292] =============================
[    0.645294] WARNING: suspicious RCU usage
[    0.645296] 5.5.4-stable #17 Not tainted
[    0.645297] -----------------------------
[    0.645299] net/ipv4/ipmr.c:136 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@...il.com>
---
 net/ipv4/ipmr.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 99c864eb6e34..950ffe9943da 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -109,9 +109,10 @@ static void mroute_clean_tables(struct mr_table *mrt, int flags);
 static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IP_MROUTE_MULTIPLE_TABLES
-#define ipmr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
-				lockdep_rtnl_is_held())
+#define ipmr_for_each_table(mrt, net)					\
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list,	\
+				lockdep_rtnl_is_held() ||		\
+				lockdep_is_held(&pernet_ops_rwsem))
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1