2022-05-10 19:37:34

by Thomas Pfaff

Subject: [PATCH] tty: Remove pointless synchronize_irq() in uart_port_shutdown()

From: Thomas Pfaff <[email protected]>

Calling synchronize_irq() after free_irq() is pointless, the context to
the irq is already lost.
It was noticed while creating the bugfix "genirq: Synchronize interrupt
thread startup".

Signed-off-by: Thomas Pfaff <[email protected]>
---
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 57840cf90388..b76e76e650ba 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -1704,12 +1704,6 @@ static void uart_port_shutdown(struct tty_port *port)
*/
if (uport)
uport->ops->shutdown(uport);
-
- /*
- * Ensure that the IRQ handler isn't running on another CPU.
- */
- if (uport)
- synchronize_irq(uport->irq);
}

static int uart_carrier_raised(struct tty_port *port)

2022-05-11 02:50:55

by Thomas Gleixner

Subject: Re: [PATCH] tty: Remove pointless synchronize_irq() in uart_port_shutdown()

On Tue, May 10 2022 at 15:54, Thomas Pfaff wrote:
> From: Thomas Pfaff <[email protected]>
>
> Calling synchronize_irq() after free_irq() is pointless, the context to
> the irq is already lost.
> It was noticed while creating the bugfix "genirq: Synchronize interrupt
> thread startup".
>
> Signed-off-by: Thomas Pfaff <[email protected]>

Reviewed-by: Thomas Gleixner <[email protected]>

2022-05-11 09:23:21

by Jiri Slaby

Subject: Re: [PATCH] tty: Remove pointless synchronize_irq() in uart_port_shutdown()

On 10. 05. 22, 15:54, Thomas Pfaff wrote:
> From: Thomas Pfaff <[email protected]>
>
> Calling synchronize_irq() after free_irq() is pointless, the context to
> the irq is already lost.
> It was noticed while creating the bugfix "genirq: Synchronize interrupt
> thread startup".

That's correct for most drivers. But some drivers don't call free_irq()
in ->shutdown(). So you likely have to move the synchronization to them.
By a quick grep, I found icom, jsm, sccnxp, sifive, sunhv, and sunzilog.

> Signed-off-by: Thomas Pfaff <[email protected]>
> ---
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 57840cf90388..b76e76e650ba 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1704,12 +1704,6 @@ static void uart_port_shutdown(struct tty_port *port)
> */
> if (uport)
> uport->ops->shutdown(uport);
> -
> - /*
> - * Ensure that the IRQ handler isn't running on another CPU.
> - */
> - if (uport)
> - synchronize_irq(uport->irq);
> }
>
> static int uart_carrier_raised(struct tty_port *port)
>
>


--
js
suse labs

2022-05-11 09:36:11

by Thomas Pfaff

Subject: Re: [PATCH] tty: Remove pointless synchronize_irq() in uart_port_shutdown()

On Wed, 11 May 2022, Jiri Slaby wrote:

> On 10. 05. 22, 15:54, Thomas Pfaff wrote:
> > From: Thomas Pfaff <[email protected]>
> >
> > Calling synchronize_irq() after free_irq() is pointless, the context to
> > the irq is already lost.
> > It was noticed while creating the bugfix "genirq: Synchronize interrupt
> > thread startup".
>
> That's correct for most drivers. But some drivers don't call free_irq() in
> ->shutdown(). So you likely have to move the synchronization to them. By a
> quick grep, I found icom, jsm, sccnxp, sifive, sunhv, and sunzilog.
>

Sorry, I did not check all the drivers.
Then I would keep it in serial_core, as it does not hurt anymore.

Thanks,
Thomas