linux-kernel - Re: [RFC][PATCH 0/7] improve printk reliability

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Message-ID: <1324466604.10752.0.camel@twins>
Date:	Wed, 21 Dec 2011 12:23:24 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ted Ts'o <tytso@....edu>, Greg KH <greg@...ah.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	akpm@...ux-foundation.org,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [RFC][PATCH 0/7] improve printk reliability

On Wed, 2011-12-21 at 11:57 +0100, Peter Zijlstra wrote:
> Hi,
> 
> So these are my current efforts to make my own console output more
> reliable. I've hit every deadlock described in this series and a few
> more.
> 
> With these patches applied I can printk() and WARN() from inside 
> scheduler context and not have my machine deadlock, even without the 
> aid of early_printk().
> 
> While I'll go an remove the sole printk() I found in the scheduler
> so that we don't have to rely on the console doing this, it is good
> to have a reliable console that can do this.
> 
> As it stands some of the patches, the semaphore one in particular,
> are really too ugly to live so I won't push those but wanted to share
> anyway.
> 
> Debugging this was 'fun', and I really hope to not have to do it
> again :-)

Also, these patches enable lockdep over printk(), allowing lockdep to
detect previously undetected deadlocks with console implementations,
irrespective of rq->lock.


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