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serial: stm32: fix a deadlock in set_termios

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[ Upstream commit 436c979360 ]

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: 6cf61b9bd7 ("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>
This commit is contained in:
Erwan Le Ray 2021-03-04 17:23:02 +01:00 • committed by Greg Kroah-Hartman
commit 1f308f65d8
1 changed files with 6 additions and 6 deletions
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12
drivers/tty/serial/stm32-usart.c
View file

@ -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)