On Mon, 22 Oct 2012, Ming Lei wrote:
> +void pm_runtime_set_memalloc_noio(struct device *dev, bool enable)
> +{
> + dev->power.memalloc_noio_resume = enable;
> +
> + if (!dev->parent)
> + return;
> +
> + if (enable) {
> + pm_runtime_set_memalloc_noio(dev->parent, 1);
> + } else {
> + /* only clear the flag for one device if all
> + * children of the device don't set the flag.
> + */
> + if (device_for_each_child(dev->parent, NULL,
> + dev_memalloc_noio))
> + return;
> +
> + pm_runtime_set_memalloc_noio(dev->parent, 0);
> + }
> +}
> +EXPORT_SYMBOL_GPL(pm_runtime_set_memalloc_noio);
Tail recursion should be implemented as a loop, not as an explicit
recursion. That is, the function should be:
void pm_runtime_set_memalloc_noio(struct device *dev, bool enable)
{
do {
dev->power.memalloc_noio_resume = enable;
if (!enable) {
/*
* Don't clear the parent's flag if any of the
* parent's children have their flag set.
*/
if (device_for_each_child(dev->parent, NULL,
dev_memalloc_noio))
return;
}
dev = dev->parent;
} while (dev);
}
except that you need to add locking, for two reasons:
There's a race. What happens if another child sets the flag
between the time device_for_each_child() runs and the next loop
iteration?
Even without a race, access to bitfields is not SMP-safe
without locking.
Alan Stern
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