linux-kernel - Re: [PATCH printk v5 1/1] printk: extend console

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Date:   Wed, 4 May 2022 08:52:14 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     John Ogness <john.ogness@...utronix.de>,
        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,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-amlogic@...ts.infradead.org
Subject: Re: [PATCH printk v5 1/1] printk: extend console_lock for
 per-console locking

Hi John,

On 04.05.2022 07:56, John Ogness wrote:
> On 2022-05-03, Marek Szyprowski <m.szyprowski@...sung.com> wrote:
>>> I suppose if you login via ssh and check /proc/interrupts, then type
>>> some things over serial, then check /proc/interrupts again, you will
>>> see there have been no interrupts for the uart. But interrupts for
>>> other devices are happening. Is this correct?
>> Right. The counter for ttyAML0 is not increased when lockup happens
>> and I type something to the uart console.
> Hmmm. This would imply that the interrupts are disabled fo the UART.
>
> Just to be sure that we haven't corrupted something in the driver, if
> you make the following change, everything works, right?
>
> --------- BEGIN PATCH ------
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index c7973266b176..1eaa323e335c 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -3578,7 +3578,7 @@ static int __init printk_activate_kthreads(void)
>   	struct console *con;
>   
>   	console_lock();
> -	printk_kthreads_available = true;
> +	//printk_kthreads_available = true;
>   	for_each_console(con)
>   		printk_start_kthread(con);
>   	console_unlock();
> --------- END PATCH ------
>
> The above change will cause the kthreads to not print and instead always
> fallback to the direct method.

With the above change console always works.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland