RE: [PATCH 1/1] tty: serial: samsung: add spin_lock for interrupt and console_write

Jaewon Kim
2022-04-05T06:40:59Z

Hello

On 22. 4. 5. 14:01, Greg Kroah-Hartman wrote:
> On Tue, Apr 05, 2022 at 12:38:54PM +0900, Jaewon Kim wrote:
> > The console_write and IRQ handler can run concurrently.
> > Problems may occurs console_write is continuously executed while the
> > IRQ handler is running.
> >
> > Signed-off-by: Jaewon Kim <jaewon02.kim@samsung.com>
> > ---
> > drivers/tty/serial/samsung_tty.c | 14 ++++++++++++++
> > 1 file changed, 14 insertions(+)
>
> What commit does this fix?

This is not an issue caused by anohter commits.
There was potential issue from the beginning.

Other drivers were fixed, but samsung_tty was not.
PL011 patch : https://lkml.org/lkml/2012/2/1/495

>
> >
> > diff --git a/drivers/tty/serial/samsung_tty.c
> > b/drivers/tty/serial/samsung_tty.c
> > index e1585fbae909..d362e8e114f1 100644
> > --- a/drivers/tty/serial/samsung_tty.c
> > +++ b/drivers/tty/serial/samsung_tty.c
> > @@ -2480,12 +2480,26 @@ s3c24xx_serial_console_write(struct console *co, const char *s,
> > unsigned int count)
> > {
> > unsigned int ucon = rd_regl(cons_uart, S3C2410_UCON);
> > + unsigned long flags;
> > + int locked = 1;
>
> bool?

It is return value of spin_trylock()
I used int because mose drivers used int.
If you guide to change int to bool, I will change it.

>
> >
> > /* not possible to xmit on unconfigured port */
> > if (!s3c24xx_port_configured(ucon))
> > return;
> >
> > + local_irq_save(flags);
> > + if (cons_uart->sysrq)
> > + locked = 0;
> > + else if (oops_in_progress)
> > + locked = spin_trylock(&cons_uart->lock);
> > + else
> > + spin_lock(&cons_uart->lock);
> > +
> > uart_console_write(cons_uart, s, count,
> > s3c24xx_serial_console_putchar);
> > +
> > + if (locked)
> > + spin_unlock(&cons_uart->lock);
> > + local_irq_restore(flags);
>
> Why is irq_save required as well as a spinlock?

No special reason.
I will change spin_trylock() -? spin_trylock_irqsave().
spin_lock -> spin_lock_irqsave().
And, remove local_irq_save/restore.
It looks more clean.

>
> thanks,
>
> greg k-h

Thanks
Jaewon Kim