linux-kernel - Re: printk() vs tty

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Message-ID: <20111214094643.GA8115@elte.hu>
Date:	Wed, 14 Dec 2011 10:46:43 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Greg KH <greg@...ah.com>, Theodore Ts'o <tytso@....edu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: printk() vs tty_io


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, 2011-12-14 at 07:59 +0100, Ingo Molnar wrote:
> 
> > btw., would be nice to also somehow realeasify those debug 
> > hacks to preserve them for eternity - doing all lockdep 
> > output as earlyprintk while keeping printks working is a 
> > great way to debug printk() itself.
> > 
> > Those printk lockups also took a *lot* of time for me to 
> > bisect.
> 
> Yeah, they're horrible.. took me long enough to reproduce, and 
> even now I know how its not easy.
> 
> Anyway, I just posted the two patches that make lockdep do 
> early_printk(), they're not too horrid. [...]

Given how crutial lockdep is to analyzing lockups, i think this 
decoupling from printk() innards is a good idea in general.

[ It also rhymes well with the general principles of lockdep, to 
  create all of its infrastructure from scratch, to be able to 
  use it everywhere. ]

The small lprintk() ugliness we can live with i think.

Thanks,

	Ingo
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