Hello, I notice that the patch is not applied in upstream. Is it missed or any other problems? Thank you! > On Mon, Sep 06, 2021 at 05:42:00PM +0800, Ziyang Xuan wrote: >> The conclusion "j1939_session_deactivate() should be called with a >> session ref-count of at least 2" is incorrect. In some concurrent >> scenarios, j1939_session_deactivate can be called with the session >> ref-count less than 2. But there is not any problem because it >> will check the session active state before session putting in >> j1939_session_deactivate_locked(). >> >> Here is the concurrent scenario of the problem reported by syzbot >> and my reproduction log. >> >> cpu0 cpu1 >> j1939_xtp_rx_eoma >> j1939_xtp_rx_abort_one >> j1939_session_get_by_addr [kref == 2] >> j1939_session_get_by_addr [kref == 3] >> j1939_session_deactivate [kref == 2] >> j1939_session_put [kref == 1] >> j1939_session_completed >> j1939_session_deactivate >> WARN_ON_ONCE(kref < 2) >> > > Ok, I see, this warning makes sense only if session will actually be > deactivated. > > Acked-by: Oleksij Rempel <o.rempel@xxxxxxxxxxxxxx> > > Thank you! > >> ===================================================== >> WARNING: CPU: 1 PID: 21 at net/can/j1939/transport.c:1088 j1939_session_deactivate+0x5f/0x70 >> CPU: 1 PID: 21 Comm: ksoftirqd/1 Not tainted 5.14.0-rc7+ #32 >> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1 04/01/2014 >> RIP: 0010:j1939_session_deactivate+0x5f/0x70 >> Call Trace: >> j1939_session_deactivate_activate_next+0x11/0x28 >> j1939_xtp_rx_eoma+0x12a/0x180 >> j1939_tp_recv+0x4a2/0x510 >> j1939_can_recv+0x226/0x380 >> can_rcv_filter+0xf8/0x220 >> can_receive+0x102/0x220 >> ? process_backlog+0xf0/0x2c0 >> can_rcv+0x53/0xf0 >> __netif_receive_skb_one_core+0x67/0x90 >> ? process_backlog+0x97/0x2c0 >> __netif_receive_skb+0x22/0x80 >> >> Fixes: 0c71437dd50d ("can: j1939: j1939_session_deactivate(): clarify lifetime of session object") >> Reported-by: syzbot+9981a614060dcee6eeca@xxxxxxxxxxxxxxxxxxxxxxxxx >> Signed-off-by: Ziyang Xuan <william.xuanziyang@xxxxxxxxxx> >> --- >> net/can/j1939/transport.c | 4 ---- >> 1 file changed, 4 deletions(-) >> >> diff --git a/net/can/j1939/transport.c b/net/can/j1939/transport.c >> index bdc95bd7a851..0f8309314075 100644 >> --- a/net/can/j1939/transport.c >> +++ b/net/can/j1939/transport.c >> @@ -1079,10 +1079,6 @@ static bool j1939_session_deactivate(struct j1939_session *session) >> bool active; >> >> j1939_session_list_lock(priv); >> - /* This function should be called with a session ref-count of at >> - * least 2. >> - */ >> - WARN_ON_ONCE(kref_read(&session->kref) < 2); >> active = j1939_session_deactivate_locked(session); >> j1939_session_list_unlock(priv); >> >> -- >> 2.25.1 >> >> >