Messages in this thread | | | Date | Fri, 17 Jul 2009 17:41:28 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm: add gfp mask checking for __get_free_pages() |
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On Sat, 4 Jul 2009 11:09:50 +0900 Akinobu Mita <akinobu.mita@gmail.com> 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 <akinobu.mita@gmail.com> > --- > 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().
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