On Thu, 31 Aug 2017 14:23:45 +0200, Anna-Maria Gleixner wrote:
From: Thomas Gleixner tglx@linutronix.de
The tasklet is used to defer the execution of snd_pcm_period_elapsed() to the softirq context. Using the CLOCK_MONOTONIC_SOFT base invokes the timer callback in softirq context as well which renders the tasklet useless.
Signed-off-by: Thomas Gleixner tglx@linutronix.de Signed-off-by: Anna-Maria Gleixner anna-maria@linutronix.de Cc: Jaroslav Kysela perex@perex.cz Cc: Takashi Iwai tiwai@suse.com Cc: Takashi Sakamoto o-takashi@sakamocchi.jp Cc: alsa-devel@alsa-project.org
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.
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.
thanks,
Takashi
--- 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; }