From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756898AbcK3Ib2 (ORCPT ); Wed, 30 Nov 2016 03:31:28 -0500 Received: from www381.your-server.de ([78.46.137.84]:46931 "EHLO www381.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755581AbcK3IbT (ORCPT ); Wed, 30 Nov 2016 03:31:19 -0500 Subject: Re: [PATCH 1/1] ALSA: SOC: DMA: increment buffer pointer atomically To: Jiada Wang , perex@perex.cz, tiwai@suse.com References: <20161130082221.15399-1-jiada_wang@mentor.com> Cc: alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, apape@de.adit-jv.com From: Lars-Peter Clausen Message-ID: <36d5025d-d327-878d-7f2e-5bf0c457581d@metafoo.de> Date: Wed, 30 Nov 2016 09:30:36 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Icedove/45.4.0 MIME-Version: 1.0 In-Reply-To: <20161130082221.15399-1-jiada_wang@mentor.com> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit X-Authenticated-Sender: lars@metafoo.de Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/2016 09:22 AM, Jiada Wang wrote: > From: Andreas Pape > > Setting pointer and afterwards check for wrap around leads > to the possibility of returning the inconsistent pointer position. > This patch increments buffer pointer atomically to avoid this issue. Makes sense. > > Signed-off-by: Andreas Pape > Signed-off-by: Jiada Wang > --- > sound/core/pcm_dmaengine.c | 8 +++++--- > 1 file changed, 5 insertions(+), 3 deletions(-) > > diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c > index 8eb58c7..6f6da11 100644 > --- a/sound/core/pcm_dmaengine.c > +++ b/sound/core/pcm_dmaengine.c > @@ -139,12 +139,14 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_set_config_from_dai_data); > > static void dmaengine_pcm_dma_complete(void *arg) > { > + unsigned int new_pos; > struct snd_pcm_substream *substream = arg; > struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream); > > - prtd->pos += snd_pcm_lib_period_bytes(substream); > - if (prtd->pos >= snd_pcm_lib_buffer_bytes(substream)) > - prtd->pos = 0; > + new_pos = prtd->pos + snd_pcm_lib_period_bytes(substream); > + if (new_pos >= snd_pcm_lib_buffer_bytes(substream)) > + new_pos = 0; > + prtd->pos = new_pos; But to really make it atomic I think this needs READ_ONCE/WRITE_ONCE.