linux-kernel - Re: [PATCH] lockdep: fix spurious 'inconsistent lock state' warning

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Date:	Mon, 18 Aug 2008 09:42:21 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dmitry Baryshkov <dbaryshkov@...il.com>
Cc:	linux-kernel@...r.kernel.org, peterz@...radead.org,
	mingo@...hat.com, Alexander Viro <viro@....linux.org.uk>
Subject: Re: [PATCH] lockdep: fix spurious 'inconsistent lock state' warning

* Dmitry Baryshkov <dbaryshkov@...il.com> wrote:

> Since f82b217e3513fe3af342c0f3ee1494e86250c21c lockdep can output 
> spurious warnings related to hwirqs due to hardirq_off shrinkage from 
> int to bit-sized flag. Guard it with double negation to fix the 
> warning.
> 
> Signed-off-by: Dmitry Baryshkov <dbaryshkov@...il.com>

good spotting! Applied to tip/core/urgent, thanks Dmitry.

I'm wondering, is there any way to teach gcc some sanity here - a safer 
variant of bitfields, that is just not allowed to overflow into or 
corrupt nearby fields? The fact that a benign looking hlock->state = 15 
can corrupt other fields worries me quite a bit. Valid C semantics or 
not, this is a totally dangerous construct. The space savings are very 
real though, so it would be nice to get 'safer bitfields', somehow.

	Ingo
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