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Date: Sun, 12 Oct 2008 19:12:11 -0400 From: Arjan van de Ven <arjan@...radead.org> To: Andrey Borzenkov <arvidjaar@...l.ru> Cc: Oliver Neukum <oliver@...kum.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: when spin_lock_irq (as opposed to spin_lock_irqsave) is appropriate? On Sun, 12 Oct 2008 15:48:00 +0400 Andrey Borzenkov <arvidjaar@...l.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 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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