From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B81AC49ED7 for ; Thu, 19 Sep 2019 09:20:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DDCCD21929 for ; Thu, 19 Sep 2019 09:20:20 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731539AbfISJUU (ORCPT ); Thu, 19 Sep 2019 05:20:20 -0400 Received: from mx1.emlix.com ([188.40.240.192]:57352 "EHLO mx1.emlix.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730839AbfISJUU (ORCPT ); Thu, 19 Sep 2019 05:20:20 -0400 Received: from mailer.emlix.com (unknown [81.20.119.6]) (using TLSv1.2 with cipher ADH-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.emlix.com (Postfix) with ESMTPS id 3D96C603BE; Thu, 19 Sep 2019 11:20:17 +0200 (CEST) Subject: Re: [PATCH 1/4] dmaengine: imx-sdma: fix buffer ownership To: Lucas Stach , linux-kernel@vger.kernel.org Cc: linux-serial@vger.kernel.org, shawnguo@kernel.org, s.hauer@pengutronix.de, jslaby@suse.com, vkoul@kernel.org, linux-imx@nxp.com, kernel@pengutronix.de, gregkh@linuxfoundation.org, dmaengine@vger.kernel.org, dan.j.williams@intel.com, festevam@gmail.com, linux-arm-kernel@lists.infradead.org References: <20190911144943.21554-1-philipp.puschmann@emlix.com> <20190911144943.21554-2-philipp.puschmann@emlix.com> <9bcf315369449a025828410396935b679aae14bf.camel@pengutronix.de> From: Philipp Puschmann Openpgp: preference=signencrypt Message-ID: Date: Thu, 19 Sep 2019 11:20:16 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <9bcf315369449a025828410396935b679aae14bf.camel@pengutronix.de> Content-Type: text/plain; charset=utf-8 Content-Language: de-DE Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Am 16.09.19 um 16:17 schrieb Lucas Stach: > On Mi, 2019-09-11 at 16:49 +0200, Philipp Puschmann wrote: >> BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the buffer, >> when 0 ARM owns it. When processing the buffers in >> sdma_update_channel_loop the ownership of the currently processed buffer >> was set to SDMA again before running the callback function of the the >> buffer and while the sdma script may be running in parallel. So there was >> the possibility to get the buffer overwritten by SDMA before it has been >> processed by kernel leading to kind of random errors in the upper layers, >> e.g. bluetooth. >> >> It may be further a good idea to make the status struct member volatile or >> access it using writel or similar to rule out that the compiler sets the >> BD_DONE flag before the callback routine has finished. >> >> Signed-off-by: Philipp Puschmann >> --- >> drivers/dma/imx-sdma.c | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c >> index a01f4b5d793c..1abb14ff394d 100644 >> --- a/drivers/dma/imx-sdma.c >> +++ b/drivers/dma/imx-sdma.c >> @@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac) >> */ >> >> desc->chn_real_count = bd->mode.count; >> - bd->mode.status |= BD_DONE; >> bd->mode.count = desc->period_len; >> desc->buf_ptail = desc->buf_tail; >> desc->buf_tail = (desc->buf_tail + 1) % desc->num_bd; >> @@ -817,6 +816,8 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac) >> dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL); >> spin_lock(&sdmac->vc.lock); > > To address your comment from the second paragraph of the commit message > there should be a dma_wmb() here before changing the status flag. > > Regards, > Lucas Hi Lucas, thanks for your feedback. I will apply the hints to v2 of the patches. Regards, Philipp > >> + bd->mode.status |= BD_DONE; >> + >> if (error) >> sdmac->status = old_status; >> } >