ALSA/dummy: Replace tasklet with softirq hrtimer

The tasklet is used to defer the execution of snd_pcm_period_elapsed() to
the softirq context. Using the HRTIMER_MODE_SOFT mode invokes the timer
callback in softirq context as well which renders the tasklet useless.

[o-takashi: avoid stall due to a call of hrtimer_cancel() on a callback of hrtimer]

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Gleixner <anna-maria@linutronix.de>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Jaroslav Kysela <perex@perex.cz>
Cc: John Stultz <john.stultz@linaro.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Takashi Iwai <tiwai@suse.com>
Cc: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Cc: alsa-devel@alsa-project.org
Cc: keescook@chromium.org
Link: http://lkml.kernel.org/r/20171221104205.7269-35-anna-maria@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 12 insertions, 15 deletions

diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
index 7b2b1f766b00..6ad2ff57833d 100644
--- a/sound/drivers/dummy.c
+++ b/sound/drivers/dummy.c
@@ -375,17 +375,9 @@ struct dummy_hrtimer_pcm {
         ktime_t period_time;
         atomic_t running;
         struct hrtimer timer;
-        struct tasklet_struct tasklet;
         struct snd_pcm_substream *substream;
 };
 
-static void dummy_hrtimer_pcm_elapsed(unsigned long priv)
-{
-        struct dummy_hrtimer_pcm *dpcm = (struct dummy_hrtimer_pcm *)priv;
-        if (atomic_read(&dpcm->running))
-                snd_pcm_period_elapsed(dpcm->substream);
-}
-
 static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer)
 {
         struct dummy_hrtimer_pcm *dpcm;
@@ -393,7 +385,14 @@ static enum hrtimer_restart dummy_hrtimer_callback(struct hrtimer *timer)
         dpcm = container_of(timer, struct dummy_hrtimer_pcm, timer);
         if (!atomic_read(&dpcm->running))
                 return HRTIMER_NORESTART;
-        tasklet_schedule(&dpcm->tasklet);
+        /*
+         * In cases of XRUN and draining, 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;
 }
@@ -403,7 +402,7 @@ static int dummy_hrtimer_start(struct snd_pcm_substream *substream)
         struct dummy_hrtimer_pcm *dpcm = substream->runtime->private_data;
 
         dpcm->base_time = hrtimer_cb_get_time(&dpcm->timer);
-        hrtimer_start(&dpcm->timer, dpcm->period_time, HRTIMER_MODE_REL);
+        hrtimer_start(&dpcm->timer, dpcm->period_time, HRTIMER_MODE_REL_SOFT);
         atomic_set(&dpcm->running, 1);
         return 0;
 }
@@ -413,14 +412,14 @@ 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;
 }
 
 static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm)
 {
         hrtimer_cancel(&dpcm->timer);
-        tasklet_kill(&dpcm->tasklet);
 }
 
 static snd_pcm_uframes_t
@@ -465,12 +464,10 @@ static int dummy_hrtimer_create(struct snd_pcm_substream *substream)
         if (!dpcm)
                 return -ENOMEM;
         substream->runtime->private_data = dpcm;
-        hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+        hrtimer_init(&dpcm->timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
         dpcm->timer.function = dummy_hrtimer_callback;
         dpcm->substream = substream;
         atomic_set(&dpcm->running, 0);
-        tasklet_init(&dpcm->tasklet, dummy_hrtimer_pcm_elapsed,
-                     (unsigned long)dpcm);
         return 0;
 }