[PATCH 5.11 152/601] serial: stm32: fix a deadlock in set_termios

Greg Kroah-Hartman
2021-05-12T17:05:35Z

From: Erwan Le Ray <erwan.leray@foss.st.com>

[ Upstream commit 436c97936001776f16153771ee887f125443e974 ]

CTS/RTS GPIOs support that has been added recently to STM32 UART driver has
introduced scheduled code in a set_termios part protected by a spin lock.
This generates a potential deadlock scenario:

Chain exists of:
&irq_desc_lock_class --> console_owner --> &port_lock_key

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&port_lock_key);
lock(console_owner);
lock(&port_lock_key);
lock(&irq_desc_lock_class);

*** DEADLOCK ***
4 locks held by stty/766:

Move the scheduled code after the spinlock.

Fixes: 6cf61b9bd7cc ("tty: serial: Add modem control gpio support for STM32 UART")
Signed-off-by: Erwan Le Ray <erwan.leray@foss.st.com>
Link: https://lore.kernel.org/r/20210304162308.8984-8-erwan.leray@foss.st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/tty/serial/stm32-usart.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index 85e9a4d4e91d..44522ddc7e6d 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -827,12 +827,6 @@ static void stm32_usart_set_termios(struct uart_port *port,
cr3 |= USART_CR3_CTSE | USART_CR3_RTSE;
}

- /* Handle modem control interrupts */
- if (UART_ENABLE_MS(port, termios->c_cflag))
- stm32_usart_enable_ms(port);
- else
- stm32_usart_disable_ms(port);
-
usartdiv = DIV_ROUND_CLOSEST(port->uartclk, baud);

/*
@@ -914,6 +908,12 @@ static void stm32_usart_set_termios(struct uart_port *port,

stm32_usart_set_bits(port, ofs->cr1, BIT(cfg->uart_enable_bit));
spin_unlock_irqrestore(&port->lock, flags);
+
+ /* Handle modem control interrupts */
+ if (UART_ENABLE_MS(port, termios->c_cflag))
+ stm32_usart_enable_ms(port);
+ else
+ stm32_usart_disable_ms(port);
}

static const char *stm32_usart_type(struct uart_port *port)
--
2.30.2