Re: [PATCH] tty: serial: manage irq with spin_lock_irqsave in SiFive console

[Jiri Slaby <jirislaby@kernel.org>]

On 01. 02. 24, 7:59, Andy Chiu wrote:
> It is not safe to call spin_lock() with irq disabled on RT-linux.
> Instead, transfer the code segment to spin_lock_irqsave to make it work
> on both RT and non-RT linux.

Hi,

have you investigated what is protected by the local_irq_save() in 
there? The lock is not always taken, OTOH the interrupts are always 
disabled.

I believe the fix is not as easy as is presented below.

> Signed-off-by: Andy Chiu <andy.chiu@sifive.com>
> ---
>   drivers/tty/serial/sifive.c | 8 +++-----
>   1 file changed, 3 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/tty/serial/sifive.c b/drivers/tty/serial/sifive.c
> index fa4c9336924f..3f0ddf8bfa7b 100644
> --- a/drivers/tty/serial/sifive.c
> +++ b/drivers/tty/serial/sifive.c
> @@ -788,13 +788,12 @@ static void sifive_serial_console_write(struct console *co, const char *s,
>   	if (!ssp)
>   		return;
>   
> -	local_irq_save(flags);
>   	if (ssp->port.sysrq)
>   		locked = 0;
>   	else if (oops_in_progress)
> -		locked = spin_trylock(&ssp->port.lock);
> +		locked = spin_trylock_irqsave(&ssp->port.lock, flags);
>   	else
> -		spin_lock(&ssp->port.lock);
> +		spin_lock_irqsave(&ssp->port.lock, flags);
>   
>   	ier = __ssp_readl(ssp, SIFIVE_SERIAL_IE_OFFS);
>   	__ssp_writel(0, SIFIVE_SERIAL_IE_OFFS, ssp);
> @@ -804,8 +803,7 @@ static void sifive_serial_console_write(struct console *co, const char *s,
>   	__ssp_writel(ier, SIFIVE_SERIAL_IE_OFFS, ssp);
>   
>   	if (locked)
> -		spin_unlock(&ssp->port.lock);
> -	local_irq_restore(flags);
> +		spin_unlock_irqrestore(&ssp->port.lock, flags);
>   }
>   
>   static int __init sifive_serial_console_setup(struct console *co, char *options)

-- 
js
suse labs