Re: [PATCH] serial: stm32: optimize spin lock usage

Greg KH
2021-04-12T05:52:30Z

On Mon, Apr 12, 2021 at 12:34:21PM +0800, dillon.minfei@gmail.com wrote:
> 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);

You shouldn't have to check for this, see the other patches on the list
recently that fixed this up to not be an issue for irq handlers.

thanks,

greg k-h