linux-kernel - Re: [PATCH] printk: stop spining waiter when console resume to flush prb

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Message-ID: <YJP5MnkJ8pJevXM6@google.com>
Date:   Thu, 6 May 2021 23:12:02 +0900
From:   Sergey Senozhatsky <senozhatsky@...omium.org>
To:     Petr Mladek <pmladek@...e.com>
Cc:     Luo Jiaxing <luojiaxing@...wei.com>, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, john.ogness@...utronix.de,
        linux-kernel@...r.kernel.org, linuxarm@...wei.com,
        bobo.shaobowang@...wei.com,
        Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [PATCH] printk: stop spining waiter when console resume to flush
 prb

On (21/05/06 23:07), Sergey Senozhatsky wrote:
> 
> Can we count the number of lines that we print from the `current` context
> in console_unlock() and if after N messages there is no console_lock waiter
> waiting for the `current` to handover console lock ownership, then create
> one: schedule IRQ work that will become a console lock owner, spin on
> console lock and call console_unlock() once it acquired the ownership.
> That 'artificial' console lock owner will do the same - print N
> messages, if nothing wants to become a console lock owner then it'll
> queue another IRQ work.

Or even simpler

console_unlock()
{
	...

	if (printed_messages > limit && !console_lock_spinning_disable_and_check()) {
		printk_safe_exit_irqrestore(flags);

		console_locked = 0;
		up_console_sem();

		defer_console_output();
		return;
	}

	...
}