Re: [RFC PATCH] memory-hotplug: Add memblock_state notifier

Vasilis Liaskovitis
2012-07-23T11:06:16Z

Hi,

On Mon, Jul 23, 2012 at 05:08:04PM +0800, Wen Congyang wrote:
> > +static int memblock_state_notifier_nb(struct notifier_block *nb, unsigned long
> > + val, void *v)
> > +{
> > + struct memory_notify *arg = (struct memory_notify *)v;
> > + struct memory_block *mem = NULL;
> > + struct mem_section *ms;
> > + unsigned long section_nr;
> > +
> > + section_nr = pfn_to_section_nr(arg->start_pfn);
> > + ms = __nr_to_section(section_nr);
> > + mem = find_memory_block(ms);
> > + if (!mem)
> > + goto out;
>
> we may offline more than one memory block.
>
thanks, you are right.

> > +
> > + switch (val) {
> > + case MEM_GOING_OFFLINE:
> > + case MEM_OFFLINE:
> > + case MEM_GOING_ONLINE:
> > + case MEM_ONLINE:
> > + case MEM_CANCEL_ONLINE:
> > + case MEM_CANCEL_OFFLINE:
> > + mem->state = val;
>
> mem->state is protected by the lock mem->state_mutex, so if you want to
> update the state, you must lock mem->state_mutex. But you cannot lock it
> here, because it may cause deadlock:
>
> acpi_memhotplug sysfs interface
> ===============================================================================
> memory_block_change_state()
> lock mem->state_mutex
> memory_block_action()
> offline_pages()
> lock_memory_hotplug()
> offline_memory()
> lock_memory_hotplug() // block
> memory_notify()
> memblock_state_notifier_nb()
> ===============================================================================

good point. Maybe if memory_hotplug_lock and state_mutex locks are acquired in
the same order in the 2 code paths, this could be avoided.

> I'm writing another patch to fix it.

ok, I 'll test.
thanks,

- Vasilis