linux-kernel - Re: [PATCH 1/2] irq_flags_t: intro and core annotations

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Message-Id: <20071022130223.f7d75c31.akpm@linux-foundation.org>
Date:	Mon, 22 Oct 2007 13:02:23 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	matthew@....cx, arnd@...db.de, ralf@...ux-mips.org,
	adobriyan@...il.com, viro@....linux.org.uk,
	viro@...iv.linux.org.uk, linux-kernel@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Re: [PATCH 1/2] irq_flags_t: intro and core annotations

On Mon, 22 Oct 2007 12:56:29 -0700 (PDT)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> 
> 
> On Mon, 22 Oct 2007, Matthew Wilcox wrote:
> > 
> > We certainly don't want to encourage people to blindly make those
> > conversions ... and I've seen the results of encouraging kernel janitors
> > to do things a certain way.
> 
> There's another issue: the "irqsave/irqrestore" versions are much safer 
> than the plain "irq" versions, in case the caller already has interrupts 
> disabled. 
> 
> So anybody making the change not only would need to make the performance 
> argument, he'd better not be a janitor that blindly does the change 
> without thinking about all call-sites etc..
> 

It's almost always a bug to do spin_lock_irq() when local interrupts are
disabled.  However iirc when we've tried to add runtime debugging to catch
that, it triggered false-positives which made the idea unworkable.  I forget
where.

However what we could do is to add a new
spin_lock_irq_tell_me_if_i_goofed() which would perform that runtime check.

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