Re: Possible broken MM code in dell-laptop.c?

Pali Rohár
2015-06-16T07:15:36Z

On Tuesday 16 June 2015 08:33:46 Michal Hocko wrote:
> On Mon 15-06-15 23:27:59, Pali Rohár wrote:
> > On Monday 15 June 2015 23:18:16 Michal Hocko wrote:
> > > On Sun 14-06-15 11:05:07, Pali Rohár wrote:
> > > > Hello,
> > > >
> > > > in drivers/platform/x86/dell-laptop.c is this part of code:
> > > >
> > > > static int __init dell_init(void)
> > > > {
> > > > ...
> > > >
> > > > /*
> > > >
> > > > * Allocate buffer below 4GB for SMI data--only 32-bit physical
> > > > addr * is passed to SMI handler.
> > > > */
> > > >
> > > > bufferpage = alloc_page(GFP_KERNEL | GFP_DMA32);
> > >
> > > [...]
> > >
> > > > buffer = page_address(bufferpage);
> > >
> > > [...]
> > >
> > > > fail_rfkill:
> > > > free_page((unsigned long)bufferpage);
> > >
> > > This one should be __free_page because it consumes struct page* and
> > > it is the proper counter part for alloc_page. free_page, just to
> > > make it confusing, consumes an address which has to be translated to
> > > a struct page.
> > >
> > > I have no idea why the API has been done this way and yeah, it is
> > > really confusing.
> > >
> > > [...]
> > >
> > > > static void __exit dell_exit(void)
> > > > {
> > > > ...
> > > >
> > > > free_page((unsigned long)buffer);
> >
> > So both, either:
> >
> > free_page((unsigned long)buffer);
> >
> > or
> >
> > __free_page(bufferpage);
> >
> > is correct?
>
> Yes. Although I would use __free_page variant as both seem to be
> globally visible.
>

Michal, thank you for explaining this situation!

Darren, I will prepare patch which will fix code and use __free_page().

(Btw, execution on fail_rfkill label caused kernel panic)

--
Pali Rohár
pali.rohar@gmail.com