linux-kernel - Re: [PATCH printk v2 08/26] printk: nbcon: Implement processing in port->lock wrapper

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Message-ID: <ZdNGlzwqwdsfwwab@smile.fi.intel.com>
Date: Mon, 19 Feb 2024 14:16:23 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Petr Mladek <pmladek@...e.com>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jirislaby@...nel.org>,
	Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	Tony Lindgren <tony@...mide.com>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Justin Chen <justin.chen@...adcom.com>,
	Jiaqing Zhao <jiaqing.zhao@...ux.intel.com>,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH printk v2 08/26] printk: nbcon: Implement processing in
 port->lock wrapper

On Sun, Feb 18, 2024 at 08:03:08PM +0106, John Ogness wrote:
> Currently the port->lock wrappers uart_port_lock(),
> uart_port_unlock() (and their variants) only lock/unlock
> the spin_lock.
> 
> If the port is an nbcon console, the wrappers must also
> acquire/release the console and mark the region as unsafe. This
> allows general port->lock synchronization to be synchronized
> with the nbcon console ownership.
> 
> Add a flag to struct uart_port to track nbcon console ownership.

..

> --- a/kernel/printk/nbcon.c
> +++ b/kernel/printk/nbcon.c
> @@ -6,6 +6,7 @@
>  #include <linux/console.h>
>  #include <linux/delay.h>
>  #include <linux/slab.h>
> +#include <linux/serial_core.h>

The headers in this file is a mess. But here you can at least keep the piece
ordered, can you?

..

> +static inline bool uart_is_nbcon(struct uart_port *up)
> +{
> +	int cookie;
> +	bool ret;
> +
> +	if (!uart_console(up))
> +		return false;
> +
> +	cookie = console_srcu_read_lock();
> +	ret = (console_srcu_read_flags(up->cons) & CON_NBCON);

The outer parentheses are redundant.

> +	console_srcu_read_unlock(cookie);
> +	return ret;
> +}

..

> +void uart_nbcon_acquire(struct uart_port *up)
> +{
> +	struct console *con = up->cons;
> +	struct nbcon_context ctxt;
> +
> +	if (!uart_is_nbcon(up))
> +		return;

> +	WARN_ON_ONCE(up->nbcon_locked_port);

+ include linux/bug.h

> +	do {
> +		do {
> +			memset(&ctxt, 0, sizeof(ctxt));

+ include linux/string.h

> +			ctxt.console	= con;
> +			ctxt.prio	= NBCON_PRIO_NORMAL;
> +		} while (!nbcon_context_try_acquire(&ctxt));
> +
> +	} while (!nbcon_context_enter_unsafe(&ctxt));
> +
> +	up->nbcon_locked_port = true;
> +}
> +EXPORT_SYMBOL_GPL(uart_nbcon_acquire);

+ include linux/export.h

-- 
With Best Regards,
Andy Shevchenko