linux-kernel - Re: [PATCH printk v1 2/2] printk: Defer legacy printing when holding printk_cpu

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Message-ID: <Z1mpxhCU-WpaKJIt@pathway.suse.cz>
Date: Wed, 11 Dec 2024 16:03:34 +0100
From: Petr Mladek <pmladek@...e.com>
To: John Ogness <john.ogness@...utronix.de>
Cc: Sergey Senozhatsky <senozhatsky@...omium.org>,
	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	Rik van Riel <riel@...riel.com>, Omar Sandoval <osandov@...a.com>
Subject: Re: [PATCH printk v1 2/2] printk: Defer legacy printing when holding
 printk_cpu_sync

On Mon 2024-12-09 12:23:46, John Ogness wrote:
> The documentation of printk_cpu_sync_get() clearly states
> that the owner must never perform any activities where it waits
> for a CPU. For legacy printing there can be spinning on the
> console_lock and on the port lock. Therefore legacy printing
> must be deferred when holding the printk_cpu_sync.
> 
> Note that in the case of emergency states, atomic consoles
> are not prevented from printing when printk is deferred. This
> is appropriate because they do not spin-wait indefinitely for
> other CPUs.
> 

It might be worth adding a reference to the original report
to show that the problem is real.

Reported-by: Rik van Riel <riel@...riel.com>
Closes: https://lore.kernel.org/r/20240715232052.73eb7fb1@imladris.surriel.com

> Signed-off-by: John Ogness <john.ogness@...utronix.de>
> Fixes: 55d6af1d6688 ("lib/nmi_backtrace: explicitly serialize banner and regs")

Anyway, it looks good.

Reviewed-by: Petr Mladek <pmladek@...e.com>

Best Regards,
Petr

PS: I am going to wait few more days for eventual feedback. I'll push
    it when nobody complains.

    I could add the above mentioned references when pushing.