Commit 436c9793 authored Mar 04, 2021 by Erwan Le Ray Committed by Greg Kroah-Hartman Mar 10, 2021

serial: stm32: fix a deadlock in set_termios



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: 6cf61b9b ("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>

parent 12761869

drivers/tty/serial/stm32-usart.c

+6 −6

Original line number	Diff line number	Diff line
		@@ -829,12 +829,6 @@ 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);

		/*
		@@ -916,6 +910,12 @@ 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)