linux-kernel - Re: [PATCH 1/1] tty: serial: samsung: add spin_lock for interrupt and console

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Date:   Tue, 5 Apr 2022 07:01:52 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jaewon Kim <jaewon02.kim@...sung.com>
Cc:     Krzysztof Kozlowski <krzk@...nel.org>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-samsung-soc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Chanho Park <chanho61.park@...sung.com>
Subject: Re: [PATCH 1/1] tty: serial: samsung: add spin_lock for interrupt
 and console_write

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@...sung.com>
> ---
>  drivers/tty/serial/samsung_tty.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)

What commit does this fix?

> 
> 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?

>  
>  	/* 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?

thanks,

greg k-h