linux-kernel - Re: [announce] "kill the Big Kernel Lock (BKL)" tree

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Date:	Wed, 14 May 2008 11:41:01 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Ingo Molnar <mingo@...e.hu>
cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Alexander Viro <viro@....linux.org.uk>
Subject: Re: [announce] "kill the Big Kernel Lock (BKL)" tree

On Wed, 14 May 2008, Ingo Molnar wrote:
> 
> Linus, Alan: the increased visibility and debuggability of the BKL 
> already uncovered a rather serious regression in upstream -git. You 
> might want to cherry pick this single fix, it will apply just fine to 
> current -git:

Ok, so I'm obviously happy. This is exactly the kind of thing I would want 
to see.

That said, the way it is now set up, it's unreasonable to merge anything 
directly, and while I can cherry-pick obvious fixes this way, I do think 
we could do things better.

It should be possible to set things up so that it's a config option, and 
we can mark it EXPERIMENTAL but still merge it into the standard kernel, 
so that we'd have the debug stuff there. That would get a lot more 
coverage, especially if it all still *works*, even if the debug stuff then 
complains (ie it would be nicer if the lock itself didn't start breaking).

So for example, have CONFIG_DEBUG_BKL turn it into a mutex (and select 
mutex debugging), and get all the debug coverage that way, but then when 
somebody enters the scheduler with the lock held, first complain, but then 
auto-release it anyway. That way, bugs get found and complained about, but 
hopefully the machine still ends up working.

		Linus
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