Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933163AbbFVIIm (ORCPT ); Mon, 22 Jun 2015 04:08:42 -0400 Received: from smtprelay.synopsys.com ([198.182.60.111]:54792 "EHLO smtprelay.synopsys.com" rhost-flags-OK-FAIL-OK-FAIL) by vger.kernel.org with ESMTP id S933138AbbFVIIh (ORCPT ); Mon, 22 Jun 2015 04:08:37 -0400 From: Alexey Brodkin To: Vineet Gupta CC: "linux-kernel@vger.kernel.org" , "peppe.cavallaro@st.com" , "linux-mm@kvack.org" , "stable@vger.kernel.org" , "m.szyprowski@samsung.com" , "netdev@vger.kernel.org" , "arc-linux-dev@synopsys.com" , "linux-arch@vger.kernel.org" , "arnd@arndb.de" Subject: Re: [arc-linux-dev] [PATCH] stmmac: explicitly zero des0 & des1 on init Thread-Topic: [arc-linux-dev] [PATCH] stmmac: explicitly zero des0 & des1 on init Thread-Index: AQHQqFuZqRqw/7Lry0SLcgimlM8X+J24EwEA Date: Mon, 22 Jun 2015 08:08:31 +0000 Message-ID: <1434960510.4269.25.camel@synopsys.com> References: <1434476441-18241-1-git-send-email-abrodkin@synopsys.com> In-Reply-To: Accept-Language: en-US, ru-RU Content-Language: en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-originating-ip: [10.121.8.57] Content-Type: text/plain; charset="utf-8" Content-ID: <9C754CE371BF664B83E790960FE8A875@internal.synopsys.com> MIME-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from base64 to 8bit by nfs id t5M88q7k003583 Content-Length: 1986 Lines: 35 Hi all, On Wed, 2015-06-17 at 07:03 +0000, Vineet Gupta wrote: +CC linux-arch, linux-mm, Arnd and Marek On Tuesday 16 June 2015 11:11 PM, Alexey Brodkin wrote: Current implementtion of descriptor init procedure only takes care about ownership flag. While it is perfectly possible to have underlying memory filled with garbage on boot or driver installation. And randomly set flags in non-zeroed des0 and des1 fields may lead to unpredictable behavior of the GMAC DMA block. Solution to this problem is as simple as explicit zeroing of both des0 and des1 fields of all buffer descriptors. Signed-off-by: Alexey Brodkin Cc: Giuseppe Cavallaro Cc: arc-linux-dev@synopsys.com Cc: linux-kernel@vger.kernel.org Cc: stable@vger.kernel.org FWIW, this was causing sporadic/random networking flakiness on ARC SDP platform (scheduled for upstream inclusion in next window) This also leads to an interesting question - should arch/*/dma_alloc_coherent() and friends unconditionally zero out memory (vs. the current semantics of letting only doing it based on gfp, as requested by driver). This is the second instance we ran into stale descriptor memory, the first one was in dw_mmc driver which was recently fixed in upstream as well (although debugged independently by Alexey and using the upstream fix) http://www.spinics.net/lists/linux-mmc/msg31600.html The pros is better out of box experience (despite buggy drivers) while the cons are they remain broken and perhaps increased boot time due to extra memzero.... Probably if we already have dma_zalloc_coherent() that does explicit zeroing of returned memory then there's no need to do implicit zeroing in dma_alloc_coherent()? -Alexey ????{.n?+???????+%?????ݶ??w??{.n?+????{??G?????s?y??杶????i??????????i