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

Ilpo Järvinen
2025-05-06T12:08:56Z

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Also, you should also improve the shortlog (in Subject) to something less
vague, e.g.:

serial: 8250_dw: assert port->lock is held in dw8250_force_idle()

On Tue, 6 May 2025, Ilpo Järvinen wrote:
> 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.