linux-kernel - [PATCH net 1/2 RESEND] ipmr: Fix RCU list debugging warning

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Message-Id: <20200509072243.3141-1-frextrite@gmail.com>
Date:   Sat,  9 May 2020 12:52:43 +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 net 1/2 RESEND] ipmr: Fix RCU list debugging warning

ipmr_for_each_table() macro uses list_for_each_entry_rcu()
for traversing outside of 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 warning at boot:

[    4.319347] =============================
[    4.319349] WARNING: suspicious RCU usage
[    4.319351] 5.5.4-stable #17 Tainted: G            E
[    4.319352] -----------------------------
[    4.319354] net/ipv4/ipmr.c:1757 RCU-list traversed in non-reader section!!

Signed-off-by: Amol Grover <frextrite@...il.com>
---
 net/ipv4/ipmr.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/ipmr.c b/net/ipv4/ipmr.c
index 6e68def66822..99c864eb6e34 100644
--- a/net/ipv4/ipmr.c
+++ b/net/ipv4/ipmr.c
@@ -110,7 +110,8 @@ 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)
+	list_for_each_entry_rcu(mrt, &net->ipv4.mr_tables, list, \
+				lockdep_rtnl_is_held())
 
 static struct mr_table *ipmr_mr_table_iter(struct net *net,
 					   struct mr_table *mrt)
-- 
2.24.1