Re: [RFC PATCH v3 3/3] acpi_memhotplug: Allow eject to proceed onrebind scenario

[Toshi Kani]

On Thu, 2012-12-06 at 13:50 +0100, Rafael J. Wysocki wrote:
> On Thursday, December 06, 2012 10:30:19 AM Vasilis Liaskovitis wrote:
> > Hi,
> > On Thu, Nov 29, 2012 at 10:44:11AM -0700, Toshi Kani wrote:
> > > On Thu, 2012-11-29 at 12:04 +0100, Vasilis Liaskovitis wrote:
> > > 
> > > Yes, that's what I had in mind along with device_lock().  I think the
> > > lock is necessary to close the window.
> > > http://www.spinics.net/lists/linux-mm/msg46973.html
> > > 
> > > But as I mentioned in other email, I prefer option 3 with
> > > suppress_bind_attrs.  So, yes, please take a look to see how it works
> > > out.
> > 
> > I tested the suppress_bind_attrs and it works by simply setting it to true
> > before driver registration e.g. 
> > 
> > --- a/drivers/acpi/scan.c
> > +++ b/drivers/acpi/scan.c
> > @@ -783,7 +783,8 @@ int acpi_bus_register_driver(struct acpi_driver *driver)
> >  	driver->drv.name = driver->name;
> >  	driver->drv.bus = &acpi_bus_type;
> >  	driver->drv.owner = driver->owner;
> > -
> > +    if (!strcmp(driver->class, "memory"))
> > +        driver->drv.suppress_bind_attrs = true;
> >  	ret = driver_register(&driver->drv);
> >  	return ret;
> >  }
> > 
> > No bind/unbind sysfs files are created when using this, as expected.
> > I assume we only want to suppress for acpi_memhotplug
> > (class=ACPI_MEMORY_DEVICE_CLASS i.e. "memory") devices.
> > 
> > Is there agreement on what acpi_bus_trim behaviour and rollback (if any) we
> > want to have for the current ACPI framework (partial trim or full trim on
> > failure)?
> 
> Last time I suggested to split the trimming so that first we only unbind
> drivers (and roll back that part, ie. rebind the drivers on errors) and
> next we remove the struct acpi_device objects, just before doing the actual
> eject.  So there would be two walks of the hierarchy below the device we want
> to eject, one for driver unbinding (that can be rolled back) and one for the
> actual removal.
> 
> Toshi Kani seemed to agree with that and there were no follow-ups.

I was hoping to have a short term solution to fix the panic on
attempting to delete a kernel memory range, assuming that the memory
hot-plug feature is going to make into 3.8.  It's a blocker issue for
testing the feature.  Now that the VM patchset does not seem to make
into 3.8, I think we can step back and focus on a long term solution
toward 3.9.

I agree that we should separate resource online/offlining step and
acpi_device creation/deletion step.  It can address the panic and make
rollback easier to handle.  For 3.9, we should have a better framework
in place to handle it in general.  So, I am currently working on a
framework proposal, and hopefully able to send it out in a week or so.

Lastly, thanks Vasilis for testing the suppress_bind_attrs change.  I
think we may still need it for 3.9.

Thanks,
-Toshi

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