Re: [rtc-linux] Re: [PATCH] rtc: Make rtc_update_irq callable with irqs enabled

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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