linux-kernel - Re: stop_machine() soft lockup

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Message-ID: <20180906125637.GJ24082@hirez.programming.kicks-ass.net>
Date:   Thu, 6 Sep 2018 14:56:37 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Niklas Cassel <niklas.cassel@...aro.org>
Cc:     linux-kernel@...r.kernel.org, bjorn.andersson@...aro.org
Subject: Re: stop_machine() soft lockup

On Wed, Sep 05, 2018 at 03:45:53PM +0200, Niklas Cassel wrote:

> However, I just managed to get this lockdep splat when booting without
> earlycon and ftrace=irqsoff
> I'm not sure that it is related, but I'm planning on looking into it anyway:

That looks like your generic printk is crap splat.

I tend to use this patch-set:

  https://lkml.kernel.org/r/20170928121823.430053219@infradead.org

and have (on x86):

  earlyprintk=serial,ttyS0,115200 force_early_printk debug ignore_loglevel

That results in a printk that does pure UART bit-banging and works from
any context without issue.