From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f172.google.com (mail-pd0-f172.google.com [209.85.192.172]) by kanga.kvack.org (Postfix) with ESMTP id 9963A6B0032 for ; Tue, 16 Jun 2015 23:43:49 -0400 (EDT) Received: by pdbki1 with SMTP id ki1so28436370pdb.1 for ; Tue, 16 Jun 2015 20:43:49 -0700 (PDT) Received: from bombadil.infradead.org (bombadil.infradead.org. [2001:1868:205::9]) by mx.google.com with ESMTPS id hb1si4142523pbd.184.2015.06.16.20.43.47 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 16 Jun 2015 20:43:47 -0700 (PDT) Date: Tue, 16 Jun 2015 20:43:34 -0700 From: Darren Hart Subject: Re: Possible broken MM code in dell-laptop.c? Message-ID: <20150617034334.GB29788@vmdeb7> References: <201506141105.07171@pali> <20150615211816.GC16138@dhcp22.suse.cz> <201506152327.59907@pali> <20150616063346.GA24296@dhcp22.suse.cz> <20150616071523.GB5863@pali> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20150616071523.GB5863@pali> Sender: owner-linux-mm@kvack.org List-ID: To: Pali =?iso-8859-1?Q?Roh=E1r?= Cc: Michal Hocko , Hans de Goede , Ben Skeggs , Stuart Hayes , Matthew Garrett , Andrew Morton , platform-driver-x86@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org On Tue, Jun 16, 2015 at 09:15:23AM +0200, Pali Rohar wrote: > On Tuesday 16 June 2015 08:33:46 Michal Hocko wrote: > > On Mon 15-06-15 23:27:59, Pali Rohar wrote: > > > On Monday 15 June 2015 23:18:16 Michal Hocko wrote: > > > > On Sun 14-06-15 11:05:07, Pali Rohar 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 - thanks for the context. I'm surprised by your recommendation to use __free_page() out here in platform driver land. I'd also prefer that the driver consistently free the same address to avoid confusion. For these reasons, free_page((unsigned long)buffer) seems like the better option. Can you elaborate on why you feel __free_page() is a better choice? -- Darren Hart Intel Open Source Technology Center -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org