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
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