linux-kernel - Re: [PATCH] tty: serial: replace spin_lock_irqsave by spin

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Message-ID: <X7d85DKvisjA3nYv@localhost>
Date:   Fri, 20 Nov 2020 09:23:00 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Tian Tao <tiantao6@...ilicon.com>
Cc:     gregkh@...uxfoundation.org, jirislaby@...nel.org, afaerber@...e.de,
        manivannan.sadhasivam@...aro.org, linux-serial@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tty: serial: replace spin_lock_irqsave by spin_lock in
 hard IRQ

On Thu, Nov 19, 2020 at 05:01:29PM +0800, Tian Tao wrote:
> The code has been in a irq-disabled context since it is hard IRQ. There
> is no necessity to do it again.
> 
> Signed-off-by: Tian Tao <tiantao6@...ilicon.com>
> ---
>  drivers/tty/serial/owl-uart.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/tty/serial/owl-uart.c b/drivers/tty/serial/owl-uart.c
> index c149f8c3..472fdaf 100644
> --- a/drivers/tty/serial/owl-uart.c
> +++ b/drivers/tty/serial/owl-uart.c
> @@ -251,10 +251,9 @@ static void owl_uart_receive_chars(struct uart_port *port)
>  static irqreturn_t owl_uart_irq(int irq, void *dev_id)
>  {
>  	struct uart_port *port = dev_id;
> -	unsigned long flags;
>  	u32 stat;
>  
> -	spin_lock_irqsave(&port->lock, flags);
> +	spin_lock(&port->lock);

Same thing here; this will break with forced irq threading (i.e.
"threadirqs") since the console code can still end up being called from
interrupt context.

>  	stat = owl_uart_read(port, OWL_UART_STAT);
>  
> @@ -268,7 +267,7 @@ static irqreturn_t owl_uart_irq(int irq, void *dev_id)
>  	stat |= OWL_UART_STAT_RIP | OWL_UART_STAT_TIP;
>  	owl_uart_write(port, stat, OWL_UART_STAT);
>  
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	spin_unlock(&port->lock);
>  
>  	return IRQ_HANDLED;
>  }

Johan