linux-kernel - Re: printk NMI splat on boot

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Message-ID: <fe455126-7b33-4246-b626-44ef33013765@paulmck-laptop>
Date: Tue, 20 May 2025 23:06:16 -0700
From: "Paul E. McKenney" <paulmck@...nel.org>
To: Jens Axboe <axboe@...nel.dk>
Cc: John Ogness <john.ogness@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>, Petr Mladek <pmladek@...e.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	"senozhatsky@...omium.org" <senozhatsky@...omium.org>
Subject: Re: printk NMI splat on boot

On Tue, May 20, 2025 at 02:41:40PM -0600, Jens Axboe wrote:
> On 5/20/25 2:18 PM, Jens Axboe wrote:
> >> What values are you using for CONFIG_RCU_EXP_CPU_STALL_TIMEOUT and
> >> CONFIG_RCU_CPU_STALL_TIMEOUT?
> > 
> > CONFIG_RCU_CPU_STALL_TIMEOUT=21
> > CONFIG_RCU_EXP_CPU_STALL_TIMEOUT=2
> 
> This was =20 btw, guess it could cut a bit too much...

Just confirming that setting CONFIG_RCU_EXP_CPU_STALL_TIMEOUT to two
milliseconds is more than a bit on the aggressive side.  ;-)

Setting it to 20 milliseconds is OK for smartphone-class devices, but
to the best of my knowledge, setting it less than 21 seconds (as in
21,000 milliseconds) has not been tested on any other platform.

> Changed them to:
> 
> CONFIG_RCU_CPU_STALL_TIMEOUT=100
> CONFIG_RCU_EXP_CPU_STALL_TIMEOUT=0
> 
> and complaining is gone.

This makes it take the default, which in this case would be the specified
CONFIG_RCU_CPU_STALL_TIMEOUT value of 100 seconds.  Which is an unusually
long timeout -- mainline these days is 21 seconds and some distros still
use the old value of 60 seconds.

							Thanx, Paul