linux-kernel - Re: PREEMPT_RT (2.6.33-rt17) disabled printk-to-console after console

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Date:	Thu, 20 May 2010 11:47:32 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Sujit K M <sjt.kar@...il.com>
cc:	"Nikita V. Youshchenko" <yoush@...msu.su>,
	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: PREEMPT_RT (2.6.33-rt17) disabled printk-to-console after
 console_init

Please stop top posting !

On Thu, 20 May 2010, Sujit K M wrote:

> >>> Well, obviously it's unsafe if you remove safety checks. And if you
> >>> care to look at the changelog of kernel/printk.c you'll find out why.
> >>
> >> Hmm... did a quick look and could not find anything related there.
> >> Could you please give a pointer?

Gah, yes. The changelog of the commit is not really helpful. Let me
explain:

The console drivers might take locks, which are converted to "sleeping
locks" in preempt-rt. As a result we cannot call into those drivers
from atomic contexts. And that's what the checks in the printk code
prevent.

Hope that helps.

Thanks,

	tglx

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