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'). 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);@@ -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 o-takashi@sakamocchi.jp 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.
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 o-takashi@sakamocchi.jp --- sound/drivers/dummy.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c index 273d60c42125..9caf754c6135 100644 --- a/sound/drivers/dummy.c +++ b/sound/drivers/dummy.c @@ -387,7 +387,11 @@ static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer) if (!atomic_read(&dpcm->running)) return HRTIMER_NORESTART;
+ /* In a case of XRUN, this calls .trigger to stop PCM substream. */ snd_pcm_period_elapsed(dpcm->substream); + if (!atomic_read(&dpcm->running)) + return HRTIMER_NORESTART; + hrtimer_forward_now(timer, dpcm->period_time); return HRTIMER_RESTART; } @@ -407,7 +411,8 @@ 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); + if (!hrtimer_callback_running(&dpcm->timer)) + hrtimer_cancel(&dpcm->timer); return 0; }