drivers: tty: serial: Fix deadlock in sa1100_set_termios()

[ Upstream commit 62b2caef400c1738b6d22f636c628d9f85cd4c4c ]

There is a deadlock in sa1100_set_termios(), which is shown
below:

   (Thread 1)              |      (Thread 2)
                           | sa1100_enable_ms()
sa1100_set_termios()       |  mod_timer()
 spin_lock_irqsave() //(1) |  (wait a time)
 ...                       | sa1100_timeout()
 del_timer_sync()          |  spin_lock_irqsave() //(2)
 (wait timer to stop)      |  ...

We hold sport->port.lock in position (1) of thread 1 and
use del_timer_sync() to wait timer to stop, but timer handler
also need sport->port.lock in position (2) of thread 2. As a result,
sa1100_set_termios() will block forever.

This patch moves del_timer_sync() before spin_lock_irqsave()
in order to prevent the deadlock.

Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Link: https://lore.kernel.org/r/20220417111626.7802-1-duoming@zju.edu.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c
index f5fab1dd96bcdef3e9de16d168069f90c8a5c520..aa1cf2ae17a903de103708be42f36d5796e42f76 100644 (file)
--- a/drivers/tty/serial/sa1100.c
+++ b/drivers/tty/serial/sa1100.c
@@ -448,6 +448,8 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
        baud = uart_get_baud_rate(port, termios, old, 0, port->uartclk/16); 
        quot = uart_get_divisor(port, baud);
 
+       del_timer_sync(&sport->timer);
+
        spin_lock_irqsave(&sport->port.lock, flags);
 
        sport->port.read_status_mask &= UTSR0_TO_SM(UTSR0_TFS);
@@ -478,8 +480,6 @@ sa1100_set_termios(struct uart_port *port, struct ktermios *termios,
                                UTSR1_TO_SM(UTSR1_ROR);
        }
 
-       del_timer_sync(&sport->timer);
-
        /*
         * Update the per-port timeout.
         */