Christoph Lameter <[email protected]> wrote:
>
> On Tue, 15 Nov 2005, Andrew Morton wrote:
>
> > But lru_add_drain_per_cpu() will be called from interrupt context: the IPI
> > handler.
>
> Ahh.. thought you meant the lru_add_drain run on the local processor.
>
> > I'm asking whether it is safe for the IPI handler to reenable interupts on
> > all architectures. It might be so, but I don't recall ever having seen it
> > discussed, nor have I seen code which does it.
>
> smp_call_function is also used by the slab allocator to drain the
> pages. All the spinlocks in there and those of the page allocator (called
> for freeing pages) use spin_lock_irqsave. Why is this not used for
> lru_add_drain() and friends?
It's a microoptimisation - lru_add_drain() is always called with local irqs
enabled, so no need for irqsave.
I don't think spin_lock_irqsave() is notably more expensive than
spin_lock_irq() - the cost is in the irq disabling and in the atomic
operation.
> Maybe we need to start a new thread so that others see it?
Spose so. If we cannot convince ourselves that local_irq_enable() in an
ipi handler is safe, we need to convert any called functions to use
irqsave.
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