Re: when spin_lock_irq (as opposed to spin_lock_irqsave) is appropriate?

Arjan van de Ven
2008-10-12T23:12:23Z

On Sun, 12 Oct 2008 15:48:00 +0400
Andrey Borzenkov <arvidjaar@mail.ru> 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
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