From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758312AbcLAMtq (ORCPT ); Thu, 1 Dec 2016 07:49:46 -0500 Received: from www381.your-server.de ([78.46.137.84]:38595 "EHLO www381.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757510AbcLAMto (ORCPT ); Thu, 1 Dec 2016 07:49:44 -0500 Subject: Re: [alsa-devel] [PATCH v2 1/1] ALSA: SOC: DMA: access buffer pointer atomically To: Jiada Wang , perex@perex.cz, tiwai@suse.com References: <20161201052422.18775-1-jiada_wang@mentor.com> Cc: alsa-devel@alsa-project.org, apape@de.adit-jv.com, linux-kernel@vger.kernel.org From: Lars-Peter Clausen Message-ID: Date: Thu, 1 Dec 2016 13:49:26 +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: <20161201052422.18775-1-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 12/01/2016 06:24 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 accesses buffer pointer atomically to avoid this issue. > > v2: use READ_ONCE and WRITE_ONCE to ensure read/write of buffer pointer in > only one access > also updates snd_dmaengine_pcm_pointer_no_residue to ensure atomic > access > > Signed-off-by: Andreas Pape > Signed-off-by: Jiada Wang Thanks for the patch. Looks good to me. Reviewed-by: Lars-Peter Clausen > --- > sound/core/pcm_dmaengine.c | 10 ++++++---- > 1 file changed, 6 insertions(+), 4 deletions(-) > > diff --git a/sound/core/pcm_dmaengine.c b/sound/core/pcm_dmaengine.c > index 8eb58c7..b6255fd 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; > + WRITE_ONCE(prtd->pos, new_pos); > > snd_pcm_period_elapsed(substream); > } > @@ -235,7 +237,7 @@ EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_trigger); > snd_pcm_uframes_t snd_dmaengine_pcm_pointer_no_residue(struct snd_pcm_substream *substream) > { > struct dmaengine_pcm_runtime_data *prtd = substream_to_prtd(substream); > - return bytes_to_frames(substream->runtime, prtd->pos); > + return bytes_to_frames(substream->runtime, READ_ONCE(prtd->pos)); > } > EXPORT_SYMBOL_GPL(snd_dmaengine_pcm_pointer_no_residue); > >