linux-kernel - Re: [BUG] Threaded printk breaks early debugging

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Message-ID: <CAMdYzYoOcLhUpqOEmXQ7t90BOgYczfq0AxK5+JKQqrPo4NGgqw@mail.gmail.com>
Date:   Sun, 12 Jun 2022 09:30:57 -0400
From:   Peter Geis <pgwipeout@...il.com>
To:     Sergey Senozhatsky <senozhatsky@...omium.org>
Cc:     John Ogness <john.ogness@...utronix.de>,
        Petr Mladek <pmladek@...e.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging

On Sat, Jun 11, 2022 at 10:57 PM Sergey Senozhatsky
<senozhatsky@...omium.org> wrote:
>
> On (22/06/10 11:34), Peter Geis wrote:
> > > On 2022-06-10, Peter Geis <pgwipeout@...il.com> wrote:
> > > > However I've run into an issue debugging early boot issues. Anything
> > > > that causes the kernel threading system to die (for example here, a
> > > > NPE) causes the boot console to halt before it outputs the error.
> > >
> > > A null pointer exception should trigger a panic, which will cause printk
> > > to enter direct mode for the oops. It should be just as effective as
> > > before introducing the printing kthreads.
> >
> > This might be a side effect of the fact that this is on a low powered
> > arm64 board. I noticed with threading enabled during large bursts the
> > console drops an excessive amount of messages. It's especially
> > apparent during the handover from earlycon to the normal console.
>
> How many CPUs does it have?

Four and all are online when the error occurs.