Re: [PATCH 2/3] serial: 8250_dw: Take port lock while accessing LSR

From: Ilpo Järvinen
Date: Wed Jun 15 2022 - 06:30:46 EST


On Wed, 15 Jun 2022, Andy Shevchenko wrote:

> On Wed, Jun 15, 2022 at 12:06:50PM +0300, Ilpo Järvinen wrote:
> > Accessing LSR requires port lock because it mutates lsr_saved_flags
> > in serial_lsr_in().
>
> I got this as patch 2/3, where are the 1/3 and 3/3?

That's probably because get_maintainer.pl didn't pick you up for the other
patches and I didn't explicitly send them to you. Here they are:

https://lore.kernel.org/linux-serial/20220615090651.15340-1-ilpo.jarvinen@xxxxxxxxxxxxxxx/T/#t

> > @@ -266,7 +266,10 @@ static int dw8250_handle_irq(struct uart_port *p)
> >
> > /* Manually stop the Rx DMA transfer when acting as flow controller */
> > if (quirks & DW_UART_QUIRK_IS_DMA_FC && up->dma && up->dma->rx_running && rx_timeout) {
> > + spin_lock_irqsave(&p->lock, flags);
> > status = serial_lsr_in(up);
> > + spin_unlock_irqrestore(&p->lock, flags);
>
> This reminds me the question, why do we need to save flags here? Aren't we in
> IRQ context already? (Perhaps another patch might be issued.)

Currently serial8250_handle_irq() reads from LSR again. I guess it would
be possible to read LSR only once and pass it as a parameter. It would
require some rework though.

--
i.