netdev - [PATCH] tcp: Pass lockdep expression to RCU lists

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Date:   Wed, 19 Feb 2020 15:35:46 +0530
From:   Amol Grover <frextrite@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>,
        "David S . Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     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>, netdev@...r.kernel.org,
        Amol Grover <frextrite@...il.com>
Subject: [PATCH] tcp: Pass lockdep expression to RCU lists

tcp_cong_list is traversed using list_for_each_entry_rcu
outside an RCU read-side critical section but under the protection
of tcp_cong_list_lock.

Hence, add corresponding lockdep expression to silence false-positive
warnings, and harden RCU lists.

Signed-off-by: Amol Grover <frextrite@...il.com>
---
 net/ipv4/tcp_cong.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 3737ec096650..8d4446ed309e 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -25,7 +25,8 @@ static struct tcp_congestion_ops *tcp_ca_find(const char *name)
 {
 	struct tcp_congestion_ops *e;
 
-	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
+	list_for_each_entry_rcu(e, &tcp_cong_list, list,
+				lockdep_is_held(&tcp_cong_list_lock)) {
 		if (strcmp(e->name, name) == 0)
 			return e;
 	}
@@ -55,7 +56,8 @@ struct tcp_congestion_ops *tcp_ca_find_key(u32 key)
 {
 	struct tcp_congestion_ops *e;
 
-	list_for_each_entry_rcu(e, &tcp_cong_list, list) {
+	list_for_each_entry_rcu(e, &tcp_cong_list, list,
+				lockdep_is_held(&tcp_cong_list_lock)) {
 		if (e->key == key)
 			return e;
 	}
@@ -317,7 +319,8 @@ int tcp_set_allowed_congestion_control(char *val)
 	}
 
 	/* pass 2 clear old values */
-	list_for_each_entry_rcu(ca, &tcp_cong_list, list)
+	list_for_each_entry_rcu(ca, &tcp_cong_list, list,
+				lockdep_is_held(&tcp_cong_list_lock))
 		ca->flags &= ~TCP_CONG_NON_RESTRICTED;
 
 	/* pass 3 mark as allowed */
-- 
2.24.1