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SubjectRe: [PATCH] removal of unnecessary irq save/restore in tasklet_hi_schedule


On Wed, 26 Jul 2000, Stuart MacDonald wrote:
> >
> > No, hard-irq's _can_ be re-entered. One hard-irq cannot re-enter itself,
> > but you can have _different_ irq's enter each other. As such, to avoid
> > deadlock in on the local CPU the current code is needed..
>
> So the following is allowable?
>
> hard_irq_a() {
> ..
> hard_irq_b();
> ..
> }

Yes.

> hard_irq_b() {
> ..
> hard_irq_a();
> ..
> }

Yes.

> Then hard_irq_a has re-entered itself.

No.

Both of the above are allowable, BUT

hard_irq_a()
hard_irq_b()
hard_irq_a()

is not. We use the interrupt blocking hardware to make sure that as long
as irq A is running, further instances of irq A are blocked. OTHER
interrupts can still happen.

Linus


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