From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f175.google.com (mail-pd0-f175.google.com [209.85.192.175]) by kanga.kvack.org (Postfix) with ESMTP id B9D2B6B0036 for ; Mon, 28 Jul 2014 11:26:46 -0400 (EDT) Received: by mail-pd0-f175.google.com with SMTP id r10so10068498pdi.20 for ; Mon, 28 Jul 2014 08:26:46 -0700 (PDT) Received: from mga09.intel.com (mga09.intel.com. [134.134.136.24]) by mx.google.com with ESMTP id dn2si9104431pdb.242.2014.07.28.08.26.45 for ; Mon, 28 Jul 2014 08:26:45 -0700 (PDT) Message-ID: <53D66BB1.8080905@linux.intel.com> Date: Mon, 28 Jul 2014 08:26:41 -0700 From: Dave Hansen MIME-Version: 1.0 Subject: Re: [PATCH] mm: don't allow fault_around_bytes to be 0 References: <53D07E96.5000006@oracle.com> <1406533400-6361-1-git-send-email-a.ryabinin@samsung.com> <20140728093611.GA3975@node.dhcp.inet.fi> In-Reply-To: <20140728093611.GA3975@node.dhcp.inet.fi> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: "Kirill A. Shutemov" , Andrey Ryabinin , Sasha Levin Cc: Andrew Morton , Linus Torvalds , Andi Kleen , Matthew Wilcox , Alexander Viro , Dave Chinner , Ning Qu , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Jones , stable@vger.kernel.org, "Kirill A. Shutemov" , Mel Gorman , Rik van Riel , Konstantin Khlebnikov , Hugh Dickins On 07/28/2014 02:36 AM, Kirill A. Shutemov wrote: > +++ b/mm/memory.c > @@ -2786,7 +2786,8 @@ static int fault_around_bytes_set(void *data, u64 val) > { > if (val / PAGE_SIZE > PTRS_PER_PTE) > return -EINVAL; > - fault_around_bytes = val; > + /* rounddown_pow_of_two(0) is not defined */ > + fault_around_bytes = max(val, PAGE_SIZE); > return 0; > } It's also possible to race and have fault_around_bytes change between when fault_around_mask() and fault_around_pages() are called so that they don't match any more. The min()/max() in do_fault_around() should keep this from doing anything _too_ nasty, but it's worth thinking about at least. The safest thing to do might be to use an ACCESS_ONCE() at the beginning of do_fault_around() for fault_around_bytes and generate fault_around_mask() from the ACCESS_ONCE() result. -- 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