linux-kernel - Re: [PATCH printk v1 18/18] printk: Perform atomic flush in console_flush_on

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Message-ID: <ZDfzn4UgbWTfjWGA@alley>
Date:   Thu, 13 Apr 2023 14:20:47 +0200
From:   Petr Mladek <pmladek@...e.com>
To:     John Ogness <john.ogness@...utronix.de>
Cc:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH printk v1 18/18] printk: Perform atomic flush in
 console_flush_on_panic()

On Thu 2023-03-02 21:02:18, John Ogness wrote:
> Typically the panic() function will take care of atomic flushing the
> non-BKL consoles on panic. However, there are several users of
> console_flush_on_panic() outside of panic().
> 
> Also perform atomic flushing in console_flush_on_panic(). A new
> function cons_force_seq() is implemented to support the
> mode=CONSOLE_REPLAY_ALL feature.
> 
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3160,6 +3160,28 @@ void console_unblank(void)
>   */
>  void console_flush_on_panic(enum con_flush_mode mode)
>  {
> +	struct console *c;
> +	short flags;
> +	int cookie;
> +	u64 seq;
> +
> +	seq = prb_first_valid_seq(prb);
> +
> +	/*
> +	 * Safely flush the atomic consoles before trying to flush any
> +	 * BKL/legacy consoles.
> +	 */
> +	if (mode == CONSOLE_REPLAY_ALL) {
> +		cookie = console_srcu_read_lock();
> +		for_each_console_srcu(c) {
> +			flags = console_srcu_read_flags(c);
> +			if (flags & CON_NO_BKL)
> +				cons_force_seq(c, seq);
> +		}
> +		console_srcu_read_unlock(cookie);
> +	}
> +	cons_atomic_flush(NULL, true);
> +
>  	if (!have_bkl_console)
>  		return;
>  
> @@ -3174,12 +3196,6 @@ void console_flush_on_panic(enum con_flush_mode mode)
>  	console_may_schedule = 0;
>  
>  	if (mode == CONSOLE_REPLAY_ALL) {
> -		struct console *c;
> -		int cookie;
> -		u64 seq;
> -
> -		seq = prb_first_valid_seq(prb);
> -
>  		cookie = console_srcu_read_lock();
>  		for_each_console_srcu(c) {
>  			/*

The code in this for_each_console_srcu(c) will reset r->seq
for all consoles, including NO_BLK ones. It should do it
only for the legacy consoles.

Best Regards,
Petr