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

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Date:	Mon, 15 Jun 2015 23:18:16 +0200
From:	Michal Hocko <mhocko@...e.cz>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Hans de Goede <hdegoede@...hat.com>,
	Darren Hart <dvhart@...radead.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	Stuart Hayes <stuart_hayes@...l.com>,
	Matthew Garrett <mjg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	platform-driver-x86@...r.kernel.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: Possible broken MM code in dell-laptop.c?

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);


-- 
Michal Hocko
SUSE Labs
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