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[209.132.180.67]) by mx.google.com with ESMTP id g9si31363edg.58.2019.09.16.12.30.54; Mon, 16 Sep 2019 12:31:18 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728126AbfIPORF (ORCPT + 99 others); Mon, 16 Sep 2019 10:17:05 -0400 Received: from metis.ext.pengutronix.de ([85.220.165.71]:54903 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726821AbfIPORE (ORCPT ); Mon, 16 Sep 2019 10:17:04 -0400 Received: from kresse.hi.pengutronix.de ([2001:67c:670:100:1d::2a]) by metis.ext.pengutronix.de with esmtp (Exim 4.92) (envelope-from ) id 1i9roM-0002Kc-Go; Mon, 16 Sep 2019 16:17:02 +0200 Message-ID: <9bcf315369449a025828410396935b679aae14bf.camel@pengutronix.de> Subject: Re: [PATCH 1/4] dmaengine: imx-sdma: fix buffer ownership From: Lucas Stach To: Philipp Puschmann , 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 Date: Mon, 16 Sep 2019 16:17:00 +0200 In-Reply-To: <20190911144943.21554-2-philipp.puschmann@emlix.com> References: <20190911144943.21554-1-philipp.puschmann@emlix.com> <20190911144943.21554-2-philipp.puschmann@emlix.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.30.5-1.1 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 2001:67c:670:100:1d::2a X-SA-Exim-Mail-From: l.stach@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 > + bd->mode.status |= BD_DONE; > + > if (error) > sdmac->status = old_status; > }