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

On Tuesday 16 June 2015 08:33:46 Michal Hocko wrote:

On Mon 15-06-15 23:27:59, Pali RohA!r wrote:

quoted

On Monday 15 June 2015 23:18:16 Michal Hocko wrote:

quoted

On Sun 14-06-15 11:05:07, Pali RohA!r wrote:

quoted

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);

[...]

quoted

	buffer = page_address(bufferpage);

[...]

quoted

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.

[...]

quoted

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 RohA!r
pali.rohar@gmail.com

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