Re: [PATCH v5 3/4] serial: 8250_dw: warning on entering dw8250_force_idle unlocked

Ilpo Järvinen
2025-05-06T12:06:28Z

On Tue, 6 May 2025, Yunhui Cui wrote:

> Read UART_RX and check UART_LSR_DR in critical section. Unsure if

Unsure if -> Ensure the

> caller of dw8250_force_idle() holds port->lock. Don't acquire it
> directly to avoid deadlock. Use lockdep_assert_held_once for warning.

Add (), although the last two sentences don't seem that useful, IMO.

>
> Signed-off-by: Yunhui Cui <cuiyunhui@bytedance.com>
> ---
> drivers/tty/serial/8250/8250_dw.c | 8 ++++++++
> 1 file changed, 8 insertions(+)
>
> diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c
> index af24ec25d976..f41c4a9ed58b 100644
> --- a/drivers/tty/serial/8250/8250_dw.c
> +++ b/drivers/tty/serial/8250/8250_dw.c
> @@ -13,6 +13,7 @@
> #include <linux/delay.h>
> #include <linux/device.h>
> #include <linux/io.h>
> +#include <linux/lockdep.h>
> #include <linux/mod_devicetable.h>
> #include <linux/module.h>
> #include <linux/notifier.h>
> @@ -112,6 +113,13 @@ static void dw8250_force_idle(struct uart_port *p)
> struct uart_8250_port *up = up_to_u8250p(p);
> unsigned int lsr;
>
> + /*
> + * The serial_in(p, UART_RX) should be under port->lock, but we can't add
> + * it to avoid AA deadlock as we're unsure if serial_out*(...UART_LCR)
> + * is under port->lock.

I'm left to wonder who/what "we" is here? Could you change it something
more precise.

> + */
> + lockdep_assert_held_once(&p->lock);
> +
> serial8250_clear_and_reinit_fifos(up);
>
> /*
>

--
i.