From mboxrd@z Thu Jan 1 00:00:00 1970 From: Shengjiu Wang Subject: Re: Issue in alsa when dma complete race with pcm release Date: Tue, 7 Jul 2015 18:13:04 +0800 Message-ID: <20150707101302.GA22212@shlinux2> References: <20150703082530.GA21580@shlinux2> <55966A75.90200@metafoo.de> <20150706090113.GA4995@shlinux2> <559A7415.8000006@metafoo.de> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from na01-bl2-obe.outbound.protection.outlook.com (mail-bl2on0143.outbound.protection.outlook.com [65.55.169.143]) by alsa0.perex.cz (Postfix) with ESMTP id CD19C2618ED for ; Tue, 7 Jul 2015 13:21:52 +0200 (CEST) Content-Disposition: inline In-Reply-To: <559A7415.8000006@metafoo.de> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: alsa-devel-bounces@alsa-project.org Sender: alsa-devel-bounces@alsa-project.org To: Lars-Peter Clausen Cc: dmaengine , alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org On Mon, Jul 06, 2015 at 02:27:01PM +0200, Lars-Peter Clausen wrote: > On 07/06/2015 11:01 AM, Shengjiu Wang wrote: > >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"? > > That will be up to the dmaengine driver. But it basically comes down > to two things: > > 1) The driver needs to make sure that tasklet_schedule() is no > longer called after terminate_all() has finished. Some driver can't make sure this. The dma interrupt may come later after terminate_all. > 2) In the sync() callback call tasklet_kill() to make sure that it > has finished running > > > > >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. > > The sync() function will only wait if there is a callback scheduled, > if there is non scheduled it will return immediately. Do you have other method to resolve this issue? or simple method? Best regards wang shengjiu