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

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Message-ID: <87h7jfzygr.fsf@jogness.linutronix.de>
Date:   Thu, 06 May 2021 17:14:12 +0200
From:   John Ogness <john.ogness@...utronix.de>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>,
        Petr Mladek <pmladek@...e.com>
Cc:     Luo Jiaxing <luojiaxing@...wei.com>, sergey.senozhatsky@...il.com,
        rostedt@...dmis.org, 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 2021-05-06, Sergey Senozhatsky <senozhatsky@...omium.org> 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;
> 	}
>
> 	...
> }

Or instead to keep it suspend/resume related maybe...

 void resume_console(void)
 {
         if (!console_suspend_enabled)
                 return;
         down_console_sem();
         console_suspended = 0;
-        console_unlock();
+        console_locked = 0;
+        up_console_sem();
+        defer_console_output();
 }

John Ogness