From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 91ECB6B0012 for ; Tue, 27 Mar 2018 14:25:02 -0400 (EDT) Received: by mail-pg0-f70.google.com with SMTP id w23so11563712pgv.17 for ; Tue, 27 Mar 2018 11:25:02 -0700 (PDT) Received: from smtprelay.synopsys.com (smtprelay2.synopsys.com. [198.182.60.111]) by mx.google.com with ESMTPS id r7si1211342pgp.212.2018.03.27.11.25.01 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Mar 2018 11:25:01 -0700 (PDT) Subject: Re: dma-mapping: clearing GFP_ZERO flag caused crashes of Ethernet on arc/hsdk board. References: <1522170774.2593.9.camel@synopsys.com> From: Vineet Gupta Message-ID: Date: Tue, 27 Mar 2018 11:24:51 -0700 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Sender: owner-linux-mm@kvack.org List-ID: To: Andy Shevchenko , hch@lst.de 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" 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