[PATCH AUTOSEL 4.19 08/27] drivers: tty: serial: Fix deadlock in sa1100_set_termios()

Sasha Levin
2022-06-07T19:53:30Z

From: Duoming Zhou <duoming@zju.edu.cn>

[ 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>
---
drivers/tty/serial/sa1100.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/sa1100.c b/drivers/tty/serial/sa1100.c
index a399772be3fc..8a65fb1ce568 100644
--- a/drivers/tty/serial/sa1100.c
+++ b/drivers/tty/serial/sa1100.c
@@ -439,6 +439,8 @@ 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);
@@ -469,8 +471,6 @@ 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.
*/
--
2.35.1