linux-kernel - Re: [PATCH printk v3 11/19] printk: nbcon: Rely on kthreads for normal operation

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Message-ID: <87plqtlh2p.fsf@jogness.linutronix.de>
Date: Wed, 31 Jul 2024 17:31:02 +0206
From: John Ogness <john.ogness@...utronix.de>
To: Petr Mladek <pmladek@...e.com>
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 v3 11/19] printk: nbcon: Rely on kthreads for
 normal operation

On 2024-07-31, Petr Mladek <pmladek@...e.com> wrote:
>> @@ -4102,8 +4139,10 @@ static bool __pr_flush(struct console *con, int timeout_ms, bool reset_on_progre
>>  			 * that they make forward progress, so only increment
>>  			 * @diff for usable consoles.
>>  			 */
>> -			if (!console_is_usable(c, flags, true))
>> +			if (!console_is_usable(c, flags, true) &&
>> +			    !console_is_usable(c, flags, false)) {
>
> This looks weird. nbcon console can't make progress when
> "write_atomic" is not implemented and the kthreads are not
> running.
>
> I should be:
>
> 			if (!((console_is_usable(c, flags, true)) ||
> 			      (console_is_usable(c, flags, false) && printk_kthreads_running))) {

I would prefer to have the printk_kthreads_running check within
console_is_usable() for the !use_atomic case.

> That said. Do we really want to support nbcon consoles without
> @write_atomic() callback?

We must. Graphic consoles will not be able to implement
write_atomic(). Network and USB consoles probably will not be able to
implement it either.

John