From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752029AbdIAL6o (ORCPT ); Fri, 1 Sep 2017 07:58:44 -0400 Received: from mx2.suse.de ([195.135.220.15]:34900 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751521AbdIAL6k (ORCPT ); Fri, 1 Sep 2017 07:58:40 -0400 Date: Fri, 01 Sep 2017 13:58:38 +0200 Message-ID: From: Takashi Iwai To: Takashi Sakamoto Cc: perex@perex.cz, anna-maria@linutronix.de, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, peterz@infradead.org, mingo@redhat.com, hch@lst.org, keescook@chromium.org, john.stultz@linaro.org, tglx@linutronix.de Subject: Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer In-Reply-To: <20170901102537.8066-1-o-takashi@sakamocchi.jp> References: <20170901102537.8066-1-o-takashi@sakamocchi.jp> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI/1.14.6 (Maruoka) FLIM/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL/10.8 Emacs/25.2 (x86_64-suse-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 01 Sep 2017 12:25:37 +0200, Takashi Sakamoto wrote: > > Hi, > > On Sep 1 2017 00:36, Takashi Iwai wrote: > > I gave it at try, but it caused a kernel hang, unfortunately. > > > > The reason is that snd_pcm_period_elapased() may stop the stream > > (e.g. when reaching at the end). With this patchset, it'll lead to > > the call of hrtimer_cancel() from the hrtimer callback itself, thus it > > stalls. > > I can reproduce this bug. > > > Below is the additional fix over your patch for working around it. > > I believe it should cover most corner cases, and seems working fine > > through quick tests, so far. > > This patch looks good to me, too. But I have an alternative. > > We can use 'hrtimer_callback_running()' to detect whether to be on hrtimer > callback or not (please read '__run_hrtimer()' in 'kernel/time/hrtimer.c'). A good point, this is a better choice. > Usage of this helper function on .stop callback to skip cancellation can > avoid the stall. In this case, after stopping PCM substream, the hrtimer > callback should return HRTIMER_NORESTART to avoid restarting, as well as > your patch. Please test a patch in this message. > > > --- > > diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c > > index 273d60c42125..b5dd64e3dab1 100644 > > --- a/sound/drivers/dummy.c > > +++ b/sound/drivers/dummy.c > > @@ -375,6 +375,7 @@ struct dummy_hrtimer_pcm { > > ktime_t base_time; > > ktime_t period_time; > > atomic_t running; > > + atomic_t callback_running; > > struct hrtimer timer; > > struct snd_pcm_substream *substream; > > }; > > @@ -387,8 +388,15 @@ static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer) > > if (!atomic_read(&dpcm->running)) > > return HRTIMER_NORESTART; > > > > + atomic_inc(&dpcm->callback_running); > > snd_pcm_period_elapsed(dpcm->substream); > > + atomic_dec(&dpcm->callback_running); > > + /* may be flipped during snd_pcm_period_elapsed() */ > > + if (!atomic_read(&dpcm->running)) > > + return HRTIMER_NORESTART; > > + > > hrtimer_forward_now(timer, dpcm->period_time); > > + atomic_dec(&dpcm->callback_running); > > return HRTIMER_RESTART; > > } > > > > @@ -407,7 +415,9 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream) > > struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data; > > > > atomic_set(&dpcm->running, 0); > > - hrtimer_cancel(&dpcm->timer); > > + /* issue hrtimer_cancel() only when called outside the callback */ > > + if (!atomic_read(&dpcm->callback_running)) > > + hrtimer_cancel(&dpcm->timer); > > return 0; > > } > > > > @@ -462,6 +472,7 @@ static int dummy_hrtimer_create(struct snd_pcm_substream *substream) > > dpcm->timer.function = dummy_hrtimer_callback; > > dpcm->substream = substream; > > atomic_set(&dpcm->running, 0); > > + atomic_set(&dpcm->callback_running, 0); > > return 0; > > } > > >From 07d61ba2a1c0e06e914443225e194d99f2d8c58d Mon Sep 17 00:00:00 2001 > From: Takashi Sakamoto > Date: Fri, 1 Sep 2017 19:10:18 +0900 > Subject: [PATCH] ALSA: dummy: avoid stall due to a call of hrtimer_cancel() on > a callback of hrtimer > > A call of 'htrimer_cancel()' on a callback of hrtimer brings endless loop > because 'struct hrtimer_clock_base.running' is not NULL on the callback. > In hrtimer subsystem, this member is used to indicate the instance of > hrtimer gets callbacks and there's a helper function, > 'hrtimer_callback_running()' to check it. > > ALSA dummy driver uses hrtimer to emulate hardware interrupt per period > of PCM buffer. When XRUN occurs on PCM substream, in a call of > 'snd_pcm_period_elapsed()', 'struct snd_pcm_ops.stop()' is called to > stop the substream. In current implementation, 'hrtimer_cancel()' is > used to wait for cancellation of hrtimer. However, as described, this > brings endless loop. It's not only about XRUN. When the stream finishes the draining, it stops the stream gracefully -- that is the very normal operation. > For this problem, this commit uses 'hrtimer_callback_running()' to > detect whether to be on a callback of hrtimer or not, then skip > cancellation of hrtimer in hrtimer callbacks. Furthermore, at a case of > XRUN, hrtimer callback returns HRTIMER_NORESTART after a call of > 'snd_pcm_period_elapsed()' to discontinue hrtimr because cancellation is > skipped. > > Signed-off-by: Takashi Sakamoto It's better to fold the fix into the original patch instead of introducing a bug and fixing it. Takashi From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takashi Iwai Subject: Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer Date: Fri, 01 Sep 2017 13:58:38 +0200 Message-ID: References: <20170901102537.8066-1-o-takashi@sakamocchi.jp> Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka") Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mx1.suse.de (mx2.suse.de [195.135.220.15]) by alsa0.perex.cz (Postfix) with ESMTP id 073842676D5 for ; Fri, 1 Sep 2017 13:58:39 +0200 (CEST) In-Reply-To: <20170901102537.8066-1-o-takashi@sakamocchi.jp> 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: Takashi Sakamoto Cc: alsa-devel@alsa-project.org, keescook@chromium.org, peterz@infradead.org, linux-kernel@vger.kernel.org, mingo@redhat.com, john.stultz@linaro.org, tglx@linutronix.de, hch@lst.org, anna-maria@linutronix.de List-Id: alsa-devel@alsa-project.org On Fri, 01 Sep 2017 12:25:37 +0200, Takashi Sakamoto wrote: > > Hi, > > On Sep 1 2017 00:36, Takashi Iwai wrote: > > I gave it at try, but it caused a kernel hang, unfortunately. > > > > The reason is that snd_pcm_period_elapased() may stop the stream > > (e.g. when reaching at the end). With this patchset, it'll lead to > > the call of hrtimer_cancel() from the hrtimer callback itself, thus it > > stalls. > > I can reproduce this bug. > > > Below is the additional fix over your patch for working around it. > > I believe it should cover most corner cases, and seems working fine > > through quick tests, so far. > > This patch looks good to me, too. But I have an alternative. > > We can use 'hrtimer_callback_running()' to detect whether to be on hrtimer > callback or not (please read '__run_hrtimer()' in 'kernel/time/hrtimer.c'). A good point, this is a better choice. > Usage of this helper function on .stop callback to skip cancellation can > avoid the stall. In this case, after stopping PCM substream, the hrtimer > callback should return HRTIMER_NORESTART to avoid restarting, as well as > your patch. Please test a patch in this message. > > > --- > > diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c > > index 273d60c42125..b5dd64e3dab1 100644 > > --- a/sound/drivers/dummy.c > > +++ b/sound/drivers/dummy.c > > @@ -375,6 +375,7 @@ struct dummy_hrtimer_pcm { > > ktime_t base_time; > > ktime_t period_time; > > atomic_t running; > > + atomic_t callback_running; > > struct hrtimer timer; > > struct snd_pcm_substream *substream; > > }; > > @@ -387,8 +388,15 @@ static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer) > > if (!atomic_read(&dpcm->running)) > > return HRTIMER_NORESTART; > > > > + atomic_inc(&dpcm->callback_running); > > snd_pcm_period_elapsed(dpcm->substream); > > + atomic_dec(&dpcm->callback_running); > > + /* may be flipped during snd_pcm_period_elapsed() */ > > + if (!atomic_read(&dpcm->running)) > > + return HRTIMER_NORESTART; > > + > > hrtimer_forward_now(timer, dpcm->period_time); > > + atomic_dec(&dpcm->callback_running); > > return HRTIMER_RESTART; > > } > > > > @@ -407,7 +415,9 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream) > > struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data; > > > > atomic_set(&dpcm->running, 0); > > - hrtimer_cancel(&dpcm->timer); > > + /* issue hrtimer_cancel() only when called outside the callback */ > > + if (!atomic_read(&dpcm->callback_running)) > > + hrtimer_cancel(&dpcm->timer); > > return 0; > > } > > > > @@ -462,6 +472,7 @@ static int dummy_hrtimer_create(struct snd_pcm_substream *substream) > > dpcm->timer.function = dummy_hrtimer_callback; > > dpcm->substream = substream; > > atomic_set(&dpcm->running, 0); > > + atomic_set(&dpcm->callback_running, 0); > > return 0; > > } > > >From 07d61ba2a1c0e06e914443225e194d99f2d8c58d Mon Sep 17 00:00:00 2001 > From: Takashi Sakamoto > Date: Fri, 1 Sep 2017 19:10:18 +0900 > Subject: [PATCH] ALSA: dummy: avoid stall due to a call of hrtimer_cancel() on > a callback of hrtimer > > A call of 'htrimer_cancel()' on a callback of hrtimer brings endless loop > because 'struct hrtimer_clock_base.running' is not NULL on the callback. > In hrtimer subsystem, this member is used to indicate the instance of > hrtimer gets callbacks and there's a helper function, > 'hrtimer_callback_running()' to check it. > > ALSA dummy driver uses hrtimer to emulate hardware interrupt per period > of PCM buffer. When XRUN occurs on PCM substream, in a call of > 'snd_pcm_period_elapsed()', 'struct snd_pcm_ops.stop()' is called to > stop the substream. In current implementation, 'hrtimer_cancel()' is > used to wait for cancellation of hrtimer. However, as described, this > brings endless loop. It's not only about XRUN. When the stream finishes the draining, it stops the stream gracefully -- that is the very normal operation. > For this problem, this commit uses 'hrtimer_callback_running()' to > detect whether to be on a callback of hrtimer or not, then skip > cancellation of hrtimer in hrtimer callbacks. Furthermore, at a case of > XRUN, hrtimer callback returns HRTIMER_NORESTART after a call of > 'snd_pcm_period_elapsed()' to discontinue hrtimr because cancellation is > skipped. > > Signed-off-by: Takashi Sakamoto It's better to fold the fix into the original patch instead of introducing a bug and fixing it. Takashi