linux-kernel - Re: [RFC][PATCH] irq: remove IRQF

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Message-Id: <20090302095553.8204d808.akpm@linux-foundation.org>
Date:	Mon, 2 Mar 2009 09:55:53 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Thomas Gleixner <tglx@...utronix.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	lkml <linux-kernel@...r.kernel.org>,
	linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [RFC][PATCH] irq: remove IRQF_DISABLED

On Mon, 02 Mar 2009 13:21:17 +0100 Peter Zijlstra <peterz@...radead.org> wrote:

> 
> People are playing odd games with IRQF_DISABLED, remove it.
> 
> Its not reliable, since shared interrupt lines could disable it for you,
> and its possible and allowed for archs to disable IRQs to limit IRQ nesting.
> 
> Therefore, simply mandate that _ALL_ IRQ handlers are run with IRQs disabled.
> 
> [ This _should_ not break anything, since we've mandated that IRQ handlers
>   _must_ be able to deal with this for a _long_ time ]
> 
> IRQ handlers should be fast, no if buts and any other exceptions. We also have
> plenty instrumentation to find any offending IRQ latency sources.

Changelog is a bit cruddy.  What are these "odd games" and why are they
so serious as to warrant a fairly drastic-looking patch?

Where are these odd games being played, and what are the implications
to those codesites of having their ball taken away?  etc.

wrt the patch itself - it would make life easier if we were to leave
the IRQF_DISABLED definition in place for a while.  I'm counting 47 new
additions of references to IRQF_DISABLED in linux-next/-mm.  It would
grease the wheels a bit were these things (and out-of-tree drivers) to
not instabreak.  One could add a nice runtime warning at request_irq()
time, leave that in place until everything is fixed up.

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