Re: [PATCH] add mutex to fbdev for fb_mmap locking

[Ingo Molnar <mingo@elte.hu>]

* Linus Torvalds <torvalds@linux-foundation.org> wrote:

> On Mon, 1 Jun 2009, Krzysztof Helt wrote:
> > 
> > I will fix it.
> 
> Thanks.
> 
> > If the revert to BKL is rejected this patch may wait till 
> > 2.6.31.
> 
> Ahh, so this one helps clean up locking, but doesn't fix any 
> actual regressions? I was going to ask you about that.
> 
> Btw - one thing you could try on the whole lockdep front - and I 
> realize that this is a _total_ hack - is to try the patch below.

One thing that might be less obscure is to add:

	lockdep_off();
	...
	lockdep_on();

to around those user-copies.

Those cause lockdep to totally ignore those dependencies. It's an 
ugly hack - but at least a readable hack IMO. With big red warning 
signs, a promise to fix this ASAP, etc.

It's still much better than a big ugly revert back to the BKL (of 
course - and regardless of how late we are in the cycle) - and 
probably a bit better than the atomic-copy hack.

Or am i missing something?

	Ingo

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