From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pd0-f172.google.com (mail-pd0-f172.google.com [209.85.192.172]) by kanga.kvack.org (Postfix) with ESMTP id C813F6B0032 for ; Fri, 27 Feb 2015 20:18:57 -0500 (EST) Received: by pdbfp1 with SMTP id fp1so24895420pdb.5 for ; Fri, 27 Feb 2015 17:18:57 -0800 (PST) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id qr1si3318469pbc.45.2015.02.27.17.18.56 for (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 27 Feb 2015 17:18:57 -0800 (PST) Date: Fri, 27 Feb 2015 17:18:11 -0800 From: Andrew Morton Subject: Re: [PATCH v2] mm: cma: fix CMA aligned offset calculation Message-Id: <20150227171811.c9f6d0ca.akpm@linux-foundation.org> In-Reply-To: <54F114D0.3060306@broadcom.com> References: <1424821185-16956-1-git-send-email-dpetigara@broadcom.com> <20150227132443.e17d574d45451f10f413f065@linux-foundation.org> <54F10358.1050102@broadcom.com> <20150227155458.697b7701d0a67ff7b4f3d9cb@linux-foundation.org> <54F114D0.3060306@broadcom.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Danesh Petigara Cc: m.szyprowski@samsung.com, mina86@mina86.com, iamjoonsoo.kim@lge.com, aneesh.kumar@linux.vnet.ibm.com, laurent.pinchart+renesas@ideasonboard.com, gregory.0xf0@gmail.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org On Fri, 27 Feb 2015 17:07:28 -0800 Danesh Petigara wrote: > On 2/27/2015 3:54 PM, Andrew Morton wrote: > > On Fri, 27 Feb 2015 15:52:56 -0800 Danesh Petigara wrote: > > > >> On 2/27/2015 1:24 PM, Andrew Morton wrote: > >>> On Tue, 24 Feb 2015 15:39:45 -0800 Danesh Petigara wrote: > >>> > >>>> The CMA aligned offset calculation is incorrect for > >>>> non-zero order_per_bit values. > >>>> > >>>> For example, if cma->order_per_bit=1, cma->base_pfn= > >>>> 0x2f800000 and align_order=12, the function returns > >>>> a value of 0x17c00 instead of 0x400. > >>>> > >>>> This patch fixes the CMA aligned offset calculation. > >>> > >>> When fixing a bug please always describe the end-user visible effects > >>> of that bug. > >>> > >>> Without that information others are unable to understand why you are > >>> recommending a -stable backport. > >>> > >> > >> Thank you for the feedback. I had no crash logs to show, nevertheless, I > >> agree that a sentence describing potential effects of the bug would've > >> helped. > > > > What was the reason for adding a cc:stable? > > > > It was added since the commit that introduced the incorrect logic > (b5be83e) was already picked up by v3.19. argh. afaict the bug will, under some conditions cause cma_alloc() to report that no suitable free area is available in the arena when in fact such regions *are* available. So it's effectively a bogus ENOMEM. Correct? If so, what are the conditions under which this will occur? This isn't hard - I want to know what the patch *does*! -- 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