From mboxrd@z Thu Jan  1 00:00:00 1970
From: Shengjiu Wang <shengjiu.wang@freescale.com>
Subject: Re: Issue in alsa when dma complete race with pcm
 release
Date: Mon, 6 Jul 2015 17:01:16 +0800
Message-ID: <20150706090113.GA4995@shlinux2>
References: <20150703082530.GA21580@shlinux2> <55966A75.90200@metafoo.de>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <alsa-devel-bounces@alsa-project.org>
Received: from na01-bn1-obe.outbound.protection.outlook.com
 (mail-bn1bbn0109.outbound.protection.outlook.com [157.56.111.109])
 by alsa0.perex.cz (Postfix) with ESMTP id 73620260533
 for <alsa-devel@alsa-project.org>; Mon,  6 Jul 2015 12:09:58 +0200 (CEST)
Content-Disposition: inline
In-Reply-To: <55966A75.90200@metafoo.de>
List-Unsubscribe: <http://mailman.alsa-project.org/mailman/options/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=unsubscribe>
List-Archive: <http://mailman.alsa-project.org/pipermail/alsa-devel/>
List-Post: <mailto:alsa-devel@alsa-project.org>
List-Help: <mailto:alsa-devel-request@alsa-project.org?subject=help>
List-Subscribe: <http://mailman.alsa-project.org/mailman/listinfo/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=subscribe>
Errors-To: alsa-devel-bounces@alsa-project.org
Sender: alsa-devel-bounces@alsa-project.org
To: Lars-Peter Clausen <lars@metafoo.de>
Cc: dmaengine <dmaengine@vger.kernel.org>, alsa-devel@alsa-project.org
List-Id: alsa-devel@alsa-project.org

On Fri, Jul 03, 2015 at 12:56:53PM +0200, Lars-Peter Clausen wrote:
> On 07/03/2015 10:25 AM, Shengjiu Wang wrote:
> >Hi alsa-devel
> >
> >    There maybe a issue in ALSA when dma complete race with snd_pcm_release.
> >The pcm release and dma complete are in different thread. There is occasion
> >that dmaengine_pcm_dma_complete() is called too late, some memory has been
> >freed, the prtd is null. Then there is kernel dump.
> >
> >    Is there any solution for this issue? Thanks.
> 
> We need to introduce a synchronization primitive that allows a
> dmaengine client to synchronize to the execution of the complete
> callbacks.
> 
> terminate_all() unfortunately can't do this since terminate_all()
> might be called from within one of the complete callbacks and so
> would cause a deadlock if we'd wait for all complete callbacks to
> finish before terminate_all() returns.
> 
> So what is needed is a new function called dmaengine_sync() that
> will wait until all scheduled complete callbacks have finished. A
> call to this function needs to be put in snd_dmaengine_pcm_close()
> before the prtd is closed.
> 
> - Lars

How to check " all scheduled complete callbacks have finished"?

One concern is if add wait in snd_dmaengine_pcm_close(), which wil cause 
the snd_pcm_release is bound with dmaengine, when there is error in dma
and no callback be called. Then the snd_pcm_release will not be released.


Best regards
wang shengjiu