Re: [rtc-linux] Re: [PATCH] rtc: Make rtc_update_irq callable with irqs enabled
From: David Brownell
Date: Thu Apr 23 2009 - 15:45:46 EST
On Thursday 23 April 2009, Alessandro Zummo wrote:
>
> > If you're talking about a different patch, please forward...
>
> no patch, just theory.
>
> the question is, do we need IRQs disabled when
> calling rtc_update_irq?
If the spinlock is *ever* acquired with IRQs disabled,
it must *always* be acquired that way.
The typical use is ... from IRQ context, which will in
some cases mean IRQs disabled. QED.
> and if yes, why? to prevent what?
Consider: one context grabs spinlock with IRQs enabled.
IRQ arrives. That context tries to grab that same lock,
from the same CPU. ==> Self-deadlock.
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