Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932227AbaJVTEN (ORCPT ); Wed, 22 Oct 2014 15:04:13 -0400 Received: from mail-vc0-f177.google.com ([209.85.220.177]:61490 "EHLO mail-vc0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753250AbaJVTEM (ORCPT ); Wed, 22 Oct 2014 15:04:12 -0400 MIME-Version: 1.0 In-Reply-To: <20141022114437.72eb61ce3e2348c52ab3d1db@linux-foundation.org> References: <1413915307-20536-1-git-send-email-sasha.levin@oracle.com> <544743D6.6040103@samsung.com> <20141022114437.72eb61ce3e2348c52ab3d1db@linux-foundation.org> Date: Wed, 22 Oct 2014 23:04:10 +0400 Message-ID: Subject: Re: [PATCH] mm, hugetlb: correct bit shift in hstate_sizelog From: Andrey Ryabinin To: Andrew Morton Cc: Andrey Ryabinin , Sasha Levin , Naoya Horiguchi , aarcange@redhat.com, Mel Gorman , LKML , "linux-mm@kvack.org" Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2014-10-22 22:44 GMT+04:00 Andrew Morton : > On Wed, 22 Oct 2014 09:42:46 +0400 Andrey Ryabinin wrote: > >> On 10/21/2014 10:15 PM, Sasha Levin wrote: >> > hstate_sizelog() would shift left an int rather than long, triggering >> > undefined behaviour and passing an incorrect value when the requested >> > page size was more than 4GB, thus breaking >4GB pages. >> >> > >> > Signed-off-by: Sasha Levin >> > --- >> > include/linux/hugetlb.h | 3 ++- >> > 1 file changed, 2 insertions(+), 1 deletion(-) >> > >> > diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h >> > index 65e12a2..57e0dfd 100644 >> > --- a/include/linux/hugetlb.h >> > +++ b/include/linux/hugetlb.h >> > @@ -312,7 +312,8 @@ static inline struct hstate *hstate_sizelog(int page_size_log) >> > { >> > if (!page_size_log) >> > return &default_hstate; >> > - return size_to_hstate(1 << page_size_log); >> > + >> > + return size_to_hstate(1UL << page_size_log); >> >> That still could be undefined on 32-bits. Either use 1ULL or reduce SHM_HUGE_MASK on 32bits. >> > > But > > struct hstate *size_to_hstate(unsigned long size) > What's wrong? On 32 bits, if page_size_log >= 32, then (unsingned long)(1ULL << page_size_log) will be truncated to 0. I guess it's ok. size_to_hstate will just return NULL in that case. -- Best regards, Andrey Ryabinin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/