From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail143.messagelabs.com (mail143.messagelabs.com [216.82.254.35]) by kanga.kvack.org (Postfix) with ESMTP id E74DF6B004F for ; Fri, 17 Jul 2009 20:41:29 -0400 (EDT) Date: Fri, 17 Jul 2009 17:41:28 -0700 From: Andrew Morton Subject: Re: [PATCH] mm: add gfp mask checking for __get_free_pages() Message-Id: <20090717174128.36d00972.akpm@linux-foundation.org> In-Reply-To: <20090704020949.GA3047@localhost.localdomain> References: <20090704020949.GA3047@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Akinobu Mita Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org List-ID: On Sat, 4 Jul 2009 11:09:50 +0900 Akinobu Mita wrote: > __get_free_pages() with __GFP_HIGHMEM is not safe because the return > address cannot represent a highmem page. get_zeroed_page() already has > such a debug checking. > > Signed-off-by: Akinobu Mita > --- > mm/page_alloc.c | 24 +++++++++--------------- > 1 files changed, 9 insertions(+), 15 deletions(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index e0f2cdf..4a1a374 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1903,31 +1903,25 @@ EXPORT_SYMBOL(__alloc_pages_nodemask); > */ > unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order) > { > - struct page * page; > + 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; > return (unsigned long) page_address(page); > } > - > EXPORT_SYMBOL(__get_free_pages); > > unsigned long get_zeroed_page(gfp_t gfp_mask) > { > - struct page * page; > - > - /* > - * get_zeroed_page() returns a 32-bit address, which cannot represent > - * a highmem page > - */ > - VM_BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0); > - > - page = alloc_pages(gfp_mask | __GFP_ZERO, 0); > - if (page) > - return (unsigned long) page_address(page); > - return 0; > + return __get_free_pages(gfp_mask | __GFP_ZERO, 0); > } > - > EXPORT_SYMBOL(get_zeroed_page); > > void __pagevec_free(struct pagevec *pvec) Fair enough. I suspect we could just delete that VM_BUG_ON() - we can't go and do runtime checking for every darn programmer error, and this would be a pretty dumb one. Your patch turns get_zeroed_page() into a simple one-liner wrapper around __get_free_pages(). We could perhaps save some .text, some kernel stack and some CPU cycles by inlining get_zeroed_page(). -- 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