Re: when spin_lock_irq (as opposed to spin_lock_irqsave) isappropriate?

[Arjan van de Ven]

On Sun, 12 Oct 2008 15:48:00 +0400
Andrey Borzenkov <arvidjaar@xxxxxxx> wrote:

> On Saturday 11 October 2008, Arjan van de Ven wrote:
> [... very useful explanation omitted ...]
> > Does this answer your question?
> > 
> 
> As Oliver pointed out, part of confusion wa my asumption that _irqsave
> verion saves actual interrupt mask. It actually does not.
> 
> This leaves me with a question - how can I know whether interrupts may
> (not) be disabled at particular point? 

the _irq versions mask the interrupts in the *cpu*!
Not in the hw.
All CPUs have a flag that says "don't give me interrupts right now
please", and the spin_lock_irq(save) functions work on that flag.
And they block all interrupts (except NMI's, which are very special)

> In particular, is it safe to 
> assume that any place marked at "code may sleep" has interrupts
> enabled?

yes.
That's a good rule of thumb ;-)
Anything else is a lot of "depends"



-- 
Arjan van de Ven 	Intel Open Source Technology Centre
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/