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

[Wen Congyang]

At 2012/7/23 19:06, Vasilis Liaskovitis Wrote:
> 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.

Yes, I am trying to fix another 2 problems(also based on ishimatsu's 
patchset):
1. offline_memory() will fail if part of the memory is onlined and part 
of the memory
   is offlined.
2. notify the userspace if the memory block's status is changed

I guess this problem can be fixed together.

Thanks
Wen Congyang

> > I'm writing another patch to fix it.
>
> ok, I 'll test.
> thanks,
>
> - Vasilis
> --
> To unsubscribe from this list: send the line "unsubscribe linux-acpi" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/