From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lars-Peter Clausen Subject: Re: Issue in alsa when dma complete race with pcm release Date: Mon, 06 Jul 2015 14:27:01 +0200 Message-ID: <559A7415.8000006@metafoo.de> References: <20150703082530.GA21580@shlinux2> <55966A75.90200@metafoo.de> <20150706090113.GA4995@shlinux2> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: Received: from smtp-out-092.synserver.de (smtp-out-092.synserver.de [212.40.185.92]) by alsa0.perex.cz (Postfix) with ESMTP id 072242605C3 for ; Mon, 6 Jul 2015 14:27:03 +0200 (CEST) In-Reply-To: <20150706090113.GA4995@shlinux2> 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: Shengjiu Wang Cc: dmaengine , alsa-devel@alsa-project.org List-Id: alsa-devel@alsa-project.org 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. 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.