On Fri, Jul 17, 2015 at 01:22:04PM +0100, Mel Gorman wrote:
> int __meminit early_pfn_to_nid(unsigned long pfn)
> {
> + static DEFINE_SPINLOCK(early_pfn_lock);
> int nid;
>
> - /* The system will behave unpredictably otherwise */
> - BUG_ON(system_state != SYSTEM_BOOTING);
> + /* Avoid locking overhead during boot but hotplug must lock */
> + if (system_state != SYSTEM_BOOTING)
> + spin_lock(&early_pfn_lock);
>
> nid = __early_pfn_to_nid(pfn, &early_pfnnid_cache);
> - if (nid >= 0)
> - return nid;
> - /* just returns 0 */
> - return 0;
> + if (nid < 0)
> + nid = 0;
> +
> + if (system_state != SYSTEM_BOOTING)
> + spin_unlock(&early_pfn_lock);
> +
> + return nid;
> }
Why the conditional locking?
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