From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail144.messagelabs.com (mail144.messagelabs.com [216.82.254.51]) by kanga.kvack.org (Postfix) with ESMTP id 7B2F86B0047 for ; Mon, 2 Mar 2009 17:28:42 -0500 (EST) Date: Mon, 2 Mar 2009 14:27:57 -0800 From: Andrew Morton Subject: Re: [PATCH] mmtom : add VM_BUG_ON in __get_free_pages Message-Id: <20090302142757.1cc014aa.akpm@linux-foundation.org> In-Reply-To: <20090302183148.a4dfcc22.minchan.kim@barrios-desktop> References: <20090302183148.a4dfcc22.minchan.kim@barrios-desktop> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: MinChan Kim Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org List-ID: On Mon, 2 Mar 2009 18:31:48 +0900 MinChan Kim wrote: > > The __get_free_pages is used in many place. > Also, driver developers can use it freely due to export function. > Some developers might use it to allocate high pages by mistake. > > The __get_free_pages can allocate high page using alloc_pages, > but it can't return linear address for high page. > > Even worse, in this csse, caller can't free page which are there in high zone. > So, It would be better to add VM_BUG_ON. > > It's based on mmtom 2009-02-27-13-54. > > Signed-off-by: MinChan Kim > --- > mm/page_alloc.c | 7 +++++++ > 1 files changed, 7 insertions(+), 0 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 8294107..381056b 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1681,6 +1681,13 @@ EXPORT_SYMBOL(__alloc_pages_internal); > unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order) > { > struct page * page; > + > + /* > + * __get_free_pages() returns a 32-bit address, which cannot represent > + * a highmem page > + */ > + VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0); > + > page = alloc_pages(gfp_mask, order); > if (!page) > return 0; If someone calls __get_free_pages(__GFP_HIGHMEM) then page_address() will reliably return NULL and the caller's code will oops. Yes, there's a decent (and increasing) risk that the developer won't be testing the code on a highmem machine, but there are enough highmem machines out there that the bug should be discovered pretty quickly. So I'm not sure that this test is worth the additional overhead to a fairly frequently called function? -- 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