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From:   Amol Grover <frextrite@gmail.com>
To:     "David S . Miller" <davem@davemloft.net>,
        Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        Jakub Kicinski <kuba@kernel.org>
Cc:     linux-kernel@vger.kernel.org,
        linux-kernel-mentees@lists.linuxfoundation.org,
        Joel Fernandes <joel@joelfernandes.org>,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>,
        "Paul E . McKenney" <paulmck@kernel.org>, netdev@vger.kernel.org,
        Amol Grover <frextrite@gmail.com>
Subject: [PATCH] ip6mr: Fix RCU list debugging warning
Date:   Sat, 22 Feb 2020 22:27:27 +0530
Message-Id: <20200222165726.9330-1-frextrite@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

ip6mr_for_each_table() macro uses list_for_each_entry_rcu()
for traversing outside an RCU read side critical section
but under the protection of rtnl_mutex. Hence add the
corresponding lockdep expression to silence the following
false-positive warnings:

[    4.319479] =============================
[    4.319480] WARNING: suspicious RCU usage
[    4.319482] 5.5.4-stable #17 Tainted: G            E
[    4.319483] -----------------------------
[    4.319485] net/ipv6/ip6mr.c:1243 RCU-list traversed in non-reader section!!

[    4.456831] =============================
[    4.456832] WARNING: suspicious RCU usage
[    4.456834] 5.5.4-stable #17 Tainted: G            E
[    4.456835] -----------------------------
[    4.456837] net/ipv6/ip6mr.c:1582 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@gmail.com>
---
 net/ipv6/ip6mr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index bfa49ff70531..d6483926f449 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -97,7 +97,8 @@ static void ipmr_expire_process(struct timer_list *t);
 
 #ifdef CONFIG_IPV6_MROUTE_MULTIPLE_TABLES
 #define ip6mr_for_each_table(mrt, net) \
-	list_for_each_entry_rcu(mrt, &net->ipv6.mr6_tables, list)
+	list_for_each_entry_rcu(mrt, &net->ipv6.mr6_tables, list, \
+				lockdep_rtnl_is_held())
 
 static struct mr_table *ip6mr_mr_table_iter(struct net *net,
 					    struct mr_table *mrt)
-- 
2.24.1