From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinod Koul Subject: Re: async between dmaengine_pcm_dma_complete and snd_pcm_release Date: Thu, 10 Oct 2013 21:17:40 +0530 Message-ID: <20131010154740.GZ2954@intel.com> References: <525505C2.4070201@marvell.com> <5255119D.9020303@metafoo.de> <52551416.9020004@metafoo.de> <52552EA5.4010109@marvell.com> <52553738.9000200@metafoo.de> <20131010025408.GV2954@intel.com> <5256403E.6090803@marvell.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mga14.intel.com (mga14.intel.com [143.182.124.37]) by alsa0.perex.cz (Postfix) with ESMTP id 7866A2619E4 for ; Thu, 10 Oct 2013 18:40:46 +0200 (CEST) Content-Disposition: inline In-Reply-To: <5256403E.6090803@marvell.com> 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: Qiao Zhou Cc: "alsa-devel@alsa-project.org" , Lars-Peter Clausen , "tiwai@suse.de" , "lgirdwood@gmail.com" , Mark Brown , "zhangfei.gao@gmail.com" , "trinity.qiao.zhou@gmail.com" , Chao Xie List-Id: alsa-devel@alsa-project.org On Thu, Oct 10, 2013 at 01:50:54PM +0800, Qiao Zhou wrote: > >1. In dma driver, once terminate_all in invoked, grab the lock, disable the > >tasklet, pause/stop the dmaengine remove all the descriptors from the lists. > >This ensures that dmaengine doesnt trigger anything new. And if it does we dont > >call into client > what lock do you refer to? is it "snd_pcm_stream_lock" or a new one > in dma driver? We are ref dma driver so it would be a dma driver lock. > >2. If we get an interrupt or tasklet invoked after this, then it is the > >resposiblity of dma driver to clear interrupt and return > > > >3. While you have invoked the terminate_all you might get a callback, in that > >case the substream is still valid (you are still in TRIGGER_STOP). There should > >be no harm in calling period_elapsed, but it would be good if we detect that and > >return from here. > > > >4. My only worry is that during callback we drop the locks held, so callback can > >be running on different CPU while you process the terminate all. This is very > >racy and possibly the issue being seen in this thread. This gets complicated by > >that fact that xrun would invoke the stop thus terminate_all. > The timing is very racy. we have two platforms, of which the only > difference is that one is 2 * a9 cpu, and the other is 4 * a7 cpu. > all other components and peripherals are the same. The result is we > can't reproduce the panic issue after more than 4 days stress test > on 2-cpu platform, but can reproduce the issue in ~10 hours level on > the 4-cpu platform. The only reason I see if dma driver is NOT buggy is that you dma driver already invoked callback and on different CPU you decided to terminate the audio and call terminate_all > >>>>On the other hand that last part could get tricky as the > >>>>dmaengine_terminate_all() might be call from within the callback. > >>>It's tricky indeed in case xrun happens. we should avoid possible deadlock. > >> > >>I think we'll eventually need to versions of dmaengine_terminate_all(). A > >>sync version which makes sure that the tasklet has finished and a non-sync > >>version that only makes sure that no new callbacks are started. I think the > >>sync version should be the default with an optional async version which must > >>be used, if it can run from within the callback. So we'd call the async > >>version in the pcm_trigger callback and the sync version in the pcm_close > >>callback. > >Yes this can be done. We can name this disable_callback cmd. The cmd will tell > >dma driver to disable all callback on the channel. This can be invoked from the > >TRIGEGR_STOP and then terminate_all in the free > > > >Which dma driver are you guys using in this? I will send a patch for the core > >and pcm layer. Someone need to test on actual hardware with driver fix :) > > > I'm using the mmp_tdma driver under /drivers/dma/, and I can test > the patch on our 4-cpu platform. thanks. Ok, let me check the driver and also see what needs to be done for this -- ~Vinod