linux-kernel - Re: [PATCH tty v1 02/74] serial: core: Use lock wrappers

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Date:   Fri, 15 Sep 2023 12:26:35 +0300 (EEST)
From:   Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To:     John Ogness <john.ogness@...utronix.de>
cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        linux-serial <linux-serial@...r.kernel.org>,
        Petr Mladek <pmladek@...e.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH tty v1 02/74] serial: core: Use lock wrappers

On Thu, 14 Sep 2023, John Ogness wrote:

> From: Thomas Gleixner <tglx@...utronix.de>
> 
> When a serial port is used for kernel console output, then all
> modifications to the UART registers which are done from other contexts,
> e.g. getty, termios, are interference points for the kernel console.
> 
> So far this has been ignored and the printk output is based on the
> principle of hope. The rework of the console infrastructure which aims to
> support threaded and atomic consoles, requires to mark sections which
> modify the UART registers as unsafe. This allows the atomic write function
> to make informed decisions and eventually to restore operational state. It
> also allows to prevent the regular UART code from modifying UART registers
> while printk output is in progress.
> 
> All modifications of UART registers are guarded by the UART port lock,
> which provides an obvious synchronization point with the console
> infrastructure.
> 
> To avoid adding this functionality to all UART drivers, wrap the
> spin_[un]lock*() invocations for uart_port::lock into helper functions
> which just contain the spin_[un]lock*() invocations for now. In a
> subsequent step these helpers will gain the console synchronization
> mechanisms.
> 
> Converted with coccinelle. No functional change.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/serial_core.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
> index f1d5c0d1568c..3091c62ec37b 100644
> --- a/include/linux/serial_core.h
> +++ b/include/linux/serial_core.h
> @@ -1035,14 +1035,14 @@ static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
>  	u8 sysrq_ch;
>  
>  	if (!port->has_sysrq) {
> -		spin_unlock(&port->lock);
> +		uart_port_unlock(port);
>  		return;
>  	}
>  
>  	sysrq_ch = port->sysrq_ch;
>  	port->sysrq_ch = 0;
>  
> -	spin_unlock(&port->lock);
> +	uart_port_unlock(port);
>  
>  	if (sysrq_ch)
>  		handle_sysrq(sysrq_ch);
> @@ -1054,14 +1054,14 @@ static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port
>  	u8 sysrq_ch;
>  
>  	if (!port->has_sysrq) {
> -		spin_unlock_irqrestore(&port->lock, flags);
> +		uart_port_unlock_irqrestore(port, flags);
>  		return;
>  	}
>  
>  	sysrq_ch = port->sysrq_ch;
>  	port->sysrq_ch = 0;
>  
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  
>  	if (sysrq_ch)
>  		handle_sysrq(sysrq_ch);
> @@ -1077,12 +1077,12 @@ static inline int uart_prepare_sysrq_char(struct uart_port *port, u8 ch)
>  }
>  static inline void uart_unlock_and_check_sysrq(struct uart_port *port)
>  {
> -	spin_unlock(&port->lock);
> +	uart_port_unlock(port);
>  }
>  static inline void uart_unlock_and_check_sysrq_irqrestore(struct uart_port *port,
>  		unsigned long flags)
>  {
> -	spin_unlock_irqrestore(&port->lock, flags);
> +	uart_port_unlock_irqrestore(port, flags);
>  }
>  #endif	/* CONFIG_MAGIC_SYSRQ_SERIAL */
>  
> 

Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>

-- 
 i.