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Date:   Wed, 20 Jul 2022 14:06:45 +0300
From:   Fedor Pchelkin <>
To:     Robin van der Gracht <>,
        Oleksij Rempel <>
Cc:     Fedor Pchelkin <>,
        Pengutronix Kernel Team <>,
        Oliver Hartkopp <>,
        Marc Kleine-Budde <>,
        "David S. Miller" <>,
        Jakub Kicinski <>,
        Elenita Hinds <>,
        Kurt Van Dijck <>,,,,
        Alexey Khoroshilov <>
Subject: [PATCH] can: j1939: Remove unnecessary WARN_ON_ONCE in j1939_sk_queue_activate_next_locked()

The purpose of WARN_ON_ONCE if the session with the same parameters
has already been activated and is currently in active_session_list is
not very clear. Is this warning implemented to indicate that userspace
is doing something wrong?

As far as I can see, there are two lists: active_session_list (which
is for the whole device) and sk_session_queue (which is unique for
each j1939_sock), and the situation when we have two sessions with
the same type, addresses and destinations in two different
sk_session_queues (owned by two different sockets) is actually highly
probable - one is active and the other is willing to become active
but the j1939_session_activate() does not let that happen. It is
correct behaviour as I assume.

Found by Linux Verification Center ( with Syzkaller.

Fixes: 9d71dd0c7009 ("can: add support of SAE J1939 protocol")
Signed-off-by: Fedor Pchelkin <>
Signed-off-by: Alexey Khoroshilov <>
 net/can/j1939/socket.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/can/j1939/socket.c b/net/can/j1939/socket.c
index f5ecfdcf57b2..be4b73afa16c 100644
--- a/net/can/j1939/socket.c
+++ b/net/can/j1939/socket.c
@@ -178,7 +178,7 @@ static void j1939_sk_queue_activate_next_locked(struct j1939_session *session)
 	if (!first)
-	if (WARN_ON_ONCE(j1939_session_activate(first))) {
+	if (j1939_session_activate(first)) {
 		first->err = -EBUSY;
 		goto activate_next;
 	} else {

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