From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751805AbeC0SZD (ORCPT ); Tue, 27 Mar 2018 14:25:03 -0400 Received: from us01smtprelay-2.synopsys.com ([198.182.60.111]:40389 "EHLO smtprelay.synopsys.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751202AbeC0SZB (ORCPT ); Tue, 27 Mar 2018 14:25:01 -0400 Subject: Re: dma-mapping: clearing GFP_ZERO flag caused crashes of Ethernet on arc/hsdk board. To: Andy Shevchenko , CC: Evgeniy Didin , "jesper.nilsson@axis.com" , Alexey Brodkin , "linux-kernel@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "geert@linux-m68k.org" , "dmaengine@vger.kernel.org" , "linux-snps-arc@lists.infradead.org" , Eugeniy Paltsev , "linux-arch@vger.kernel.org" , "linux-mm@kvack.org" References: <1522170774.2593.9.camel@synopsys.com> From: Vineet Gupta Message-ID: Date: Tue, 27 Mar 2018 11:24:51 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.6.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Originating-IP: [10.10.161.84] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Christoph, Andy On 03/27/2018 11:11 AM, Andy Shevchenko wrote: > On Tue, Mar 27, 2018 at 8:12 PM, Evgeniy Didin > wrote: >> Hello, >> >> After commit 57bf5a8963f8 ("dma-mapping: clear harmful GFP_* flags in common code") we noticed problems with Ethernet controller on one of our platforms (namely ARC HSDK). >> I >> n particular we see that removal of __GFP_ZERO flag in function dma_alloc_attrs() was the culprit because in our implementation of arc_dma_alloc() we only allocate zeroed pages if >> that flag is explicitly set by the caller. Now with unconditional removal of that flag in dma_alloc_attrs() we allocate non-zeroed pages and that seem to cause problems. >> >> From >> mentioned commit message I may conclude that architectural code is supposed to always allocate zeroed pages but I cannot find any requirement of that in kernel's documentation. >> Coul >> d you please point me to that requirement if that exists at all, then we'll implement a fix in our arch code like that: [snip] > Another question why caller can't ask for zero pages explicitly? Question to whom ? The caller can ask for it - but the problem here is generic dma API code is clearing out GFP_ZERO and expecting arch code to memst unconditionally - is that expected of arch code - and is documented ? That is broken to begin with - arch dma_alloc* simply passes thru gfp flags to page allocator and doesn't muck around with them. We could in theory but doesn't seem like the right thing to do IMO. -Vineet