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

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Message-ID: <20150616101211.GA25899@amd>
Date:	Tue, 16 Jun 2015 12:12:12 +0200
From:	Pavel Machek <pavel@....cz>
To:	Pali Rohár <pali.rohar@...il.com>
Cc:	Darren Hart <dvhart@...radead.org>,
	Hans de Goede <hdegoede@...hat.com>,
	Ben Skeggs <bskeggs@...hat.com>,
	Stuart Hayes <stuart_hayes@...l.com>,
	Matthew Garrett <mjg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Michal Hocko <mhocko@...e.cz>,
	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 Mon 2015-06-15 22:42:30, Pali Rohár wrote:
> On Monday 15 June 2015 22:36:45 Darren Hart wrote:
> > On Sun, Jun 14, 2015 at 11:05:07AM +0200, 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);
> > > 	if (!bufferpage) {
> > > 	
> > > 		ret = -ENOMEM;
> > > 		goto fail_buffer;
> > > 	
> > > 	}
> > > 	buffer = page_address(bufferpage);
> > > 	
> > > 	ret = dell_setup_rfkill();
> > > 	
> > > 	if (ret) {
> > > 	
> > > 		pr_warn("Unable to setup rfkill\n");
> > > 		goto fail_rfkill;
> > > 	
> > > 	}
> > > 
> > > ...
> > > 
> > > fail_rfkill:
> > > 	free_page((unsigned long)bufferpage);
> > > 
> > > fail_buffer:
> > > ...
> > > }
> > > 
> > > Then there is another part:
> > > 
> > > static void __exit dell_exit(void)
> > > {
> > > ...
> > > 
> > > 	free_page((unsigned long)buffer);
> > 
> > I believe you are correct, and this should be bufferpage. Have you
> > observed any failures?
> 
> Rmmoding dell-laptop.ko works fine. There is no error in dmesg. I think 
> that buffer (and not bufferpage) should be passed to free_page(). So in 
> my opinion problem is at fail_rfkill: label and not in dell_exit().

You seem to be right. Interface is strange...

alloc_pages() returns struct page *,
__free_pages() takes struct page *,
free_pages() takes unsinged long.

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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