From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qc0-f173.google.com (mail-qc0-f173.google.com [209.85.216.173]) by kanga.kvack.org (Postfix) with ESMTP id 572306B0038 for ; Wed, 22 Oct 2014 14:50:32 -0400 (EDT) Received: by mail-qc0-f173.google.com with SMTP id w7so3292192qcr.4 for ; Wed, 22 Oct 2014 11:50:32 -0700 (PDT) Received: from aserp1040.oracle.com (aserp1040.oracle.com. [141.146.126.69]) by mx.google.com with ESMTPS id c3si29383648qan.79.2014.10.22.11.50.31 for (version=TLSv1 cipher=RC4-SHA bits=128/128); Wed, 22 Oct 2014 11:50:31 -0700 (PDT) Message-ID: <5447FC6E.2000207@oracle.com> Date: Wed, 22 Oct 2014 14:50:22 -0400 From: Sasha Levin MIME-Version: 1.0 Subject: Re: [PATCH] mm, hugetlb: correct bit shift in hstate_sizelog References: <1413915307-20536-1-git-send-email-sasha.levin@oracle.com> <544743D6.6040103@samsung.com> <20141022114437.72eb61ce3e2348c52ab3d1db@linux-foundation.org> In-Reply-To: <20141022114437.72eb61ce3e2348c52ab3d1db@linux-foundation.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Andrew Morton , Andrey Ryabinin Cc: n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, mgorman@suse.de, linux-kernel@vger.kernel.org, linux-mm@kvack.org On 10/22/2014 02:44 PM, Andrew Morton wrote: > 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) True, but "(1 << page_size_log)" produces an integer rather than long because "1" is an int and not long. #include int main(void) { unsigned long a, b; a = 1 << 32; b = 1UL << 32; printf("a: %lu b: %lu\n", a, b); } $ ./a.out a: 0 b: 4294967296 With the patch, size_to_hstate() gets the unsigned long it expects. Thanks, Sasha -- 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