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    Subject[PATCH 23/25 v2] ALSA/dummy: Replace tasklet with softirq hrtimer
    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
    [o-takashi: avoid stall due to a call of hrtimer_cancel() on a callback
    of hrtimer]
    Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    ---
    On 2017-09-02 10:19:45 [+0900], Takashi Sakamoto wrote:
    > Yep. I request the authors to include this
    Thank you for providing a fix.

    v1…v2: merged Takashi Sakamoto fixup of the original patch into v2.

    So this patch now is okay?

    sound/drivers/dummy.c | 23 +++++++++--------------
    1 file changed, 9 insertions(+), 14 deletions(-)

    diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
    index dd5ed037adf2..3d01fe17ed36 100644
    --- a/sound/drivers/dummy.c
    +++ b/sound/drivers/dummy.c
    @@ -376,17 +376,9 @@ 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;
    @@ -394,7 +386,12 @@ 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 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;
    }
    @@ -414,14 +411,14 @@ 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
    @@ -466,12 +463,10 @@ 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_SOFT, HRTIMER_MODE_REL);
    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;
    }

    --
    2.14.1
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