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

Michal Hocko
2015-06-16T06:34:00Z

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 Hocko
SUSE Labs