linux-kernel - Re: [PATCH 04/10] ALSA: aloop: Use always spin_lock

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Date:   Mon, 25 Mar 2019 17:07:02 +0100
From:   Takashi Iwai <tiwai@...e.de>
To:     <twischer@...adit-jv.com>
Cc:     <broonie@...nel.org>, <perex@...ex.cz>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 04/10] ALSA: aloop: Use always spin_lock_irqsave() for cable->lock

On Mon, 25 Mar 2019 17:00:38 +0100,
<twischer@...adit-jv.com> wrote:
> 
> From: Timo Wischer <twischer@...adit-jv.com>
> 
> to allow the usage of timer callbacks from interrupt context.
> For example the sound timer.

The trigger callback is already irq-disabled.  And, open/close must
not be irq-disabled OTOH.  So these changes must be superfluous.


thanks,

Takashi


> 
> Signed-off-by: Timo Wischer <twischer@...adit-jv.com>
> ---
>  sound/drivers/aloop.c | 33 +++++++++++++++++++--------------
>  1 file changed, 19 insertions(+), 14 deletions(-)
> 
> diff --git a/sound/drivers/aloop.c b/sound/drivers/aloop.c
> index 11e8ed6..c6217c4 100644
> --- a/sound/drivers/aloop.c
> +++ b/sound/drivers/aloop.c
> @@ -272,6 +272,7 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
>  	struct loopback_pcm *dpcm = runtime->private_data;
>  	struct loopback_cable *cable = dpcm->cable;
>  	int err = 0, stream = 1 << substream->stream;
> +	unsigned long flags;
>  
>  	switch (cmd) {
>  	case SNDRV_PCM_TRIGGER_START:
> @@ -281,39 +282,39 @@ static int loopback_trigger(struct snd_pcm_substream *substream, int cmd)
>  		dpcm->last_jiffies = jiffies;
>  		dpcm->pcm_rate_shift = 0;
>  		dpcm->last_drift = 0;
> -		spin_lock(&cable->lock);	
> +		spin_lock_irqsave(&cable->lock, flags);
>  		cable->running |= stream;
>  		cable->pause &= ~stream;
>  		err = loopback_timer_start(dpcm);
> -		spin_unlock(&cable->lock);
> +		spin_unlock_irqrestore(&cable->lock, flags);
>  		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>  			loopback_active_notify(dpcm);
>  		break;
>  	case SNDRV_PCM_TRIGGER_STOP:
> -		spin_lock(&cable->lock);	
> +		spin_lock_irqsave(&cable->lock, flags);
>  		cable->running &= ~stream;
>  		cable->pause &= ~stream;
>  		err = loopback_timer_stop(dpcm);
> -		spin_unlock(&cable->lock);
> +		spin_unlock_irqrestore(&cable->lock, flags);
>  		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>  			loopback_active_notify(dpcm);
>  		break;
>  	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>  	case SNDRV_PCM_TRIGGER_SUSPEND:
> -		spin_lock(&cable->lock);	
> +		spin_lock_irqsave(&cable->lock, flags);
>  		cable->pause |= stream;
>  		err = loopback_timer_stop(dpcm);
> -		spin_unlock(&cable->lock);
> +		spin_unlock_irqrestore(&cable->lock, flags);
>  		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>  			loopback_active_notify(dpcm);
>  		break;
>  	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>  	case SNDRV_PCM_TRIGGER_RESUME:
> -		spin_lock(&cable->lock);
> +		spin_lock_irqsave(&cable->lock, flags);
>  		dpcm->last_jiffies = jiffies;
>  		cable->pause &= ~stream;
>  		err = loopback_timer_start(dpcm);
> -		spin_unlock(&cable->lock);
> +		spin_unlock_irqrestore(&cable->lock, flags);
>  		if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
>  			loopback_active_notify(dpcm);
>  		break;
> @@ -557,12 +558,13 @@ static snd_pcm_uframes_t loopback_pointer(struct snd_pcm_substream *substream)
>  {
>  	struct snd_pcm_runtime *runtime = substream->runtime;
>  	struct loopback_pcm *dpcm = runtime->private_data;
> +	unsigned long flags;
>  	snd_pcm_uframes_t pos;
>  
> -	spin_lock(&dpcm->cable->lock);
> +	spin_lock_irqsave(&dpcm->cable->lock, flags);
>  	loopback_pos_update(dpcm->cable);
>  	pos = dpcm->buf_pos;
> -	spin_unlock(&dpcm->cable->lock);
> +	spin_unlock_irqrestore(&dpcm->cable->lock, flags);
>  	return bytes_to_frames(runtime, pos);
>  }
>  
> @@ -679,10 +681,12 @@ static void free_cable(struct snd_pcm_substream *substream)
>  	if (!cable)
>  		return;
>  	if (cable->streams[!substream->stream]) {
> +		unsigned long flags;
> +
>  		/* other stream is still alive */
> -		spin_lock_irq(&cable->lock);
> +		spin_lock_irqsave(&cable->lock, flags);
>  		cable->streams[substream->stream] = NULL;
> -		spin_unlock_irq(&cable->lock);
> +		spin_unlock_irqrestore(&cable->lock, flags);
>  	} else {
>  		/* free the cable */
>  		loopback->cables[substream->number][dev] = NULL;
> @@ -698,6 +702,7 @@ static int loopback_open(struct snd_pcm_substream *substream)
>  	struct loopback_cable *cable = NULL;
>  	int err = 0;
>  	int dev = get_cable_index(substream);
> +	unsigned long flags;
>  
>  	mutex_lock(&loopback->cable_lock);
>  	dpcm = kzalloc(sizeof(*dpcm), GFP_KERNEL);
> @@ -753,9 +758,9 @@ static int loopback_open(struct snd_pcm_substream *substream)
>  	else
>  		runtime->hw = cable->hw;
>  
> -	spin_lock_irq(&cable->lock);
> +	spin_lock_irqsave(&cable->lock, flags);
>  	cable->streams[substream->stream] = dpcm;
> -	spin_unlock_irq(&cable->lock);
> +	spin_unlock_irqrestore(&cable->lock, flags);
>  
>   unlock:
>  	if (err < 0) {
> -- 
> 2.7.4
> 
>