[PATCH] serial: stm32: optimize spin lock usage

dillon.minfei
2021-04-12T04:34:30Z

From: dillon min <dillon.minfei@gmail.com>

To avoid potential deadlock in spin_lock usage, change to use
spin_lock_irqsave(), spin_unlock_irqrestore() in process(thread_fn) context.
spin_lock(), spin_unlock() under handler context.

remove unused local_irq_save/restore call.

Signed-off-by: dillon min <dillon.minfei@gmail.com>
---
Was verified on stm32f469-disco board. need more test on stm32mp platform.

drivers/tty/serial/stm32-usart.c | 27 +++++++++++++++++----------
1 file changed, 17 insertions(+), 10 deletions(-)

diff --git a/drivers/tty/serial/stm32-usart.c b/drivers/tty/serial/stm32-usart.c
index b3675cf25a69..c4c859b34367 100644
--- a/drivers/tty/serial/stm32-usart.c
+++ b/drivers/tty/serial/stm32-usart.c
@@ -214,7 +214,7 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
struct tty_port *tport = &port->state->port;
struct stm32_port *stm32_port = to_stm32_port(port);
const struct stm32_usart_offsets *ofs = &stm32_port->info->ofs;
- unsigned long c;
+ unsigned long c, flags;
u32 sr;
char flag;

@@ -276,9 +276,17 @@ static void stm32_usart_receive_chars(struct uart_port *port, bool threaded)
uart_insert_char(port, sr, USART_SR_ORE, c, flag);
}

- spin_unlock(&port->lock);
+ if (threaded)
+ spin_unlock_irqrestore(&port->lock, flags);
+ else
+ spin_unlock(&port->lock);
+
tty_flip_buffer_push(tport);
- spin_lock(&port->lock);
+
+ if (threaded)
+ spin_lock_irqsave(&port->lock, flags);
+ else
+ spin_lock(&port->lock);
}

static void stm32_usart_tx_dma_complete(void *arg)
@@ -489,13 +497,14 @@ static irqreturn_t stm32_usart_threaded_interrupt(int irq, void *ptr)
{
struct uart_port *port = ptr;
struct stm32_port *stm32_port = to_stm32_port(port);
+ unsigned long flags;

- spin_lock(&port->lock);
+ spin_lock_irqsave(&port->lock, flags);

if (stm32_port->rx_ch)
stm32_usart_receive_chars(port, true);

- spin_unlock(&port->lock);
+ spin_unlock_irqrestore(&port->lock, flags);

return IRQ_HANDLED;
}
@@ -1354,13 +1363,12 @@ static void stm32_usart_console_write(struct console *co, const char *s,
u32 old_cr1, new_cr1;
int locked = 1;

- local_irq_save(flags);
if (port->sysrq)
locked = 0;
else if (oops_in_progress)
- locked = spin_trylock(&port->lock);
+ locked = spin_trylock_irqsave(&port->lock, flags);
else
- spin_lock(&port->lock);
+ spin_lock_irqsave(&port->lock, flags);

/* Save and disable interrupts, enable the transmitter */
old_cr1 = readl_relaxed(port->membase + ofs->cr1);
@@ -1374,8 +1382,7 @@ static void stm32_usart_console_write(struct console *co, const char *s,
writel_relaxed(old_cr1, port->membase + ofs->cr1);

if (locked)
- spin_unlock(&port->lock);
- local_irq_restore(flags);
+ spin_unlock_irqrestore(&port->lock, flags);
}

static int stm32_usart_console_setup(struct console *co, char *options)
--
2.7.4