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From:   madhuparnabhowmik10@gmail.com
To:     davem@davemloft.net, kuznet@ms2.inr.ac.ru, yoshfuji@linux-ipv6.org,
        kuba@kernel.org
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        sfr@canb.auug.org.au, frextrite@gmail.com, joel@joelfernandes.org,
        paulmck@kernel.org, cai@lca.pw,
        Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
Subject: [PATCH net] ipv6: Fix suspicious RCU usage warning in ip6mr
Date:   Thu, 14 May 2020 12:32:04 +0530
Message-Id: <20200514070204.3108-1-madhuparnabhowmik10@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

From: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>

This patch fixes the following warning:

=============================
WARNING: suspicious RCU usage
5.7.0-rc4-next-20200507-syzkaller #0 Not tainted
-----------------------------
net/ipv6/ip6mr.c:124 RCU-list traversed in non-reader section!!

ipmr_new_table() returns an existing table, but there is no table at
init. Therefore the condition: either holding rtnl or the list is empty
is used.

Fixes: d13fee049f ("Default enable RCU list lockdep debugging with .."): WARNING: suspicious RCU usage
Reported-by: kernel test robot <lkp@intel.com>
Suggested-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Madhuparna Bhowmik <madhuparnabhowmik10@gmail.com>
---
 net/ipv6/ip6mr.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/ipv6/ip6mr.c b/net/ipv6/ip6mr.c
index 65a54d74acc1..fbe282bb8036 100644
--- a/net/ipv6/ip6mr.c
+++ b/net/ipv6/ip6mr.c
@@ -98,7 +98,7 @@ 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, \
-				lockdep_rtnl_is_held())
+				lockdep_rtnl_is_held() ||  list_empty(&net->ipv6.mr6_tables))
 
 static struct mr_table *ip6mr_mr_table_iter(struct net *net,
 					    struct mr_table *mrt)
-- 
2.17.1