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From: John Ogness <john.ogness@linutronix.de>
To: Peter Geis <pgwipeout@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging
Date: Fri, 10 Jun 2022 17:11:15 +0206	[thread overview]
Message-ID: <87y1y48spg.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com>

Hi Peter,

On 2022-06-10, Peter Geis <pgwipeout@gmail.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.

Can you please provide a test case or patch that will trigger the
problem you refer to?

> Would it be possible to have both a kconfig option and a runtime
> option to toggle printk_fallback_preferred_direct()? Currently I've
> had to force it at all times while debugging.

It would be trivial to provide a boot parameter for this behavior, but I
think we first need to see a real problem and also see if we can fix
that problem.

John Ogness

WARNING: multiple messages have this Message-ID (diff)
From: John Ogness <john.ogness@linutronix.de>
To: Peter Geis <pgwipeout@gmail.com>
Cc: Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <senozhatsky@chromium.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	"open list:ARM/Rockchip SoC..."
	<linux-rockchip@lists.infradead.org>
Subject: Re: [BUG] Threaded printk breaks early debugging
Date: Fri, 10 Jun 2022 17:11:15 +0206	[thread overview]
Message-ID: <87y1y48spg.fsf@jogness.linutronix.de> (raw)
In-Reply-To: <CAMdYzYpF4FNTBPZsEFeWRuEwSies36QM_As8osPWZSr2q-viEA@mail.gmail.com>

Hi Peter,

On 2022-06-10, Peter Geis <pgwipeout@gmail.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.

Can you please provide a test case or patch that will trigger the
problem you refer to?

> Would it be possible to have both a kconfig option and a runtime
> option to toggle printk_fallback_preferred_direct()? Currently I've
> had to force it at all times while debugging.

It would be trivial to provide a boot parameter for this behavior, but I
think we first need to see a real problem and also see if we can fix
that problem.

John Ogness

_______________________________________________
Linux-rockchip mailing list
Linux-rockchip@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-rockchip

  reply	other threads:[~2022-06-10 15:05 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-10 12:48 [BUG] Threaded printk breaks early debugging Peter Geis
2022-06-10 12:48 ` Peter Geis
2022-06-10 15:05 ` John Ogness [this message]
2022-06-10 15:05   ` John Ogness
2022-06-10 15:34   ` Peter Geis
2022-06-10 15:34     ` Peter Geis
2022-06-12  2:57     ` Sergey Senozhatsky
2022-06-12  2:57       ` Sergey Senozhatsky
2022-06-12 13:30       ` Peter Geis
2022-06-12 13:30         ` Peter Geis
2022-06-12 23:08     ` John Ogness
2022-06-12 23:08       ` John Ogness
2022-06-12 23:30       ` Peter Geis
2022-06-12 23:30         ` Peter Geis
2022-06-13  2:23         ` John Ogness
2022-06-13  2:23           ` John Ogness
2022-06-13 15:11           ` Petr Mladek
2022-06-13 15:11             ` Petr Mladek
2022-06-13 22:20             ` Peter Geis
2022-06-13 22:20               ` Peter Geis
2022-06-14  8:38               ` Petr Mladek
2022-06-14  8:38                 ` Petr Mladek
2022-06-13 11:24         ` Petr Mladek
2022-06-13 11:24           ` Petr Mladek
2022-06-12  3:13   ` Sergey Senozhatsky
2022-06-12  3:13     ` Sergey Senozhatsky
2022-06-12 23:02     ` John Ogness
2022-06-12 23:02       ` John Ogness
2022-06-13  3:49       ` Sergey Senozhatsky
2022-06-13  3:49         ` Sergey Senozhatsky
2022-06-13  8:30         ` John Ogness
2022-06-13  8:30           ` John Ogness
2022-06-13  9:05           ` Sergey Senozhatsky
2022-06-13  9:05             ` Sergey Senozhatsky
2022-06-13 10:14             ` Petr Mladek
2022-06-13 10:14               ` Petr Mladek
2022-06-13 16:11               ` David Laight
2022-06-13 16:11                 ` David Laight
2022-06-14  8:37                 ` Petr Mladek
2022-06-14  8:37                   ` Petr Mladek

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