[04/10] ALSA: aloop: Use always spin_lock_irqsave() for cable->lock

Commit Message

Timo Wischer March 25, 2019, 4 p.m. UTC

From: Timo Wischer <[e-mail]>

to allow the usage of timer callbacks from interrupt context.
For example the sound timer.

Signed-off-by: Timo Wischer <[e-mail]>
---
 sound/drivers/aloop.c | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)

Comments

Takashi Iwai March 25, 2019, 4:07 p.m. UTC | #1

On Mon, 25 Mar 2019 17:00:38 +0100,
<[e-mail]> wrote:
> 
> From: Timo Wischer <[e-mail]>
> 
> 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 <[e-mail]>
> ---
>  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
> 
>

Timo Wischer March 25, 2019, 4:40 p.m. UTC | #2

Best regards
*Timo Wischer*
Engineering Software Base (ADITG/ESB)

Tel. [phone]
On 3/25/19 17:07, Takashi Iwai wrote:
> On Mon, 25 Mar 2019 17:00:38 +0100,
> <[e-mail]> wrote:
>> From: Timo Wischer <[e-mail]>
>>
>> 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.

Hello Takashi,

could you explain why open/close must not be irq-disabled?
I see a potential deadlock in case of free_cable() uses only spin_lock() 
instead of spin_lock_irqsave().
For example the following will be executed:

loopback_close()
free_cable()
spin_lock(&dpcm->cable->lock)
 >> Interrupted by jiffies timer IRQ before calling spin_unlock()

loopback_jiffies_timer_function()
spin_lock_irqsave(&dpcm->cable->lock)
 >> DEADLOCK due to dpcm->cable->lock is already locked

Do you also see this deadlock or do you see any reason why this could 
not happen?

Best regards

Timo

>
>
> thanks,
>
> Takashi
>
>
>> Signed-off-by: Timo Wischer <[e-mail]>
>> ---
>>   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
>>
>>

Takashi Iwai March 25, 2019, 4:58 p.m. UTC | #3

On Mon, 25 Mar 2019 17:40:23 +0100,
Timo Wischer wrote:
> 
> Best regards
> Timo Wischer
> Engineering Software Base (ADITG/ESB)
> 
> Tel. [phone]
> On 3/25/19 17:07, Takashi Iwai wrote:
> 
>     On Mon, 25 Mar 2019 17:00:38 +0100,
>     <[e-mail]> wrote:
>     
>         From: Timo Wischer <[e-mail]>
>         
>         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.
>     
> Hello Takashi,
> 
> could you explain why open/close must not be irq-disabled?

The open/close callbacks get called always in sleepable context where
you can use mutex & co gracefully.  The only non-sleepable (atomic)
context is pointer and trigger callbacks.  So it's safe to use
spin_lock() without irq in these callbacks.
OTOH, the rest (open, close,hw_params, hw_free, prepare) callbacks are
always sleepable, hence it's safe to use spin_lock_irq() (not
save/restore) variant.

When a driver declares as non-atomic via PCM flag, all callbacks
become sleepable, but this isn't the case for aloop driver.

> I see a potential deadlock in case of free_cable() uses only spin_lock()
> instead of spin_lock_irqsave().
> For example the following will be executed:
> 
> loopback_close()
> free_cable()
> spin_lock(&dpcm->cable->lock)

Which spin_lock() call?  The free_cable() calls spin_lock_irq().

> >> Interrupted by jiffies timer IRQ before calling spin_unlock()
> 
> loopback_jiffies_timer_function()
> spin_lock_irqsave(&dpcm->cable->lock)
> >> DEADLOCK due to dpcm->cable->lock is already locked
> 
> Do you also see this deadlock or do you see any reason why this could not
> happen?

If spin_lock_irq() is used in free_cable(), it must be OK.


Takashi


> Best regards
> 
> Timo
> 
>     thanks,
>     
>     Takashi
> 
>         Signed-off-by: Timo Wischer <[e-mail]>
>         ---
>          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
> 
>

Timo Wischer March 26, 2019, 8:12 a.m. UTC | #4

On 3/25/19 17:58, Takashi Iwai wrote:
> On Mon, 25 Mar 2019 17:40:23 +0100,
> Timo Wischer wrote:
>> Best regards
>> Timo Wischer
>> Engineering Software Base (ADITG/ESB)
>>
>> Tel. [phone]
>> On 3/25/19 17:07, Takashi Iwai wrote:
>>
>>      On Mon, 25 Mar 2019 17:00:38 +0100,
>>      <[e-mail]> wrote:
>>      
>>          From: Timo Wischer <[e-mail]>
>>          
>>          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.
>>      
>> Hello Takashi,
>>
>> could you explain why open/close must not be irq-disabled?
> The open/close callbacks get called always in sleepable context where
> you can use mutex & co gracefully.  The only non-sleepable (atomic)
> context is pointer and trigger callbacks.  So it's safe to use
> spin_lock() without irq in these callbacks.
> OTOH, the rest (open, close,hw_params, hw_free, prepare) callbacks are
> always sleepable, hence it's safe to use spin_lock_irq() (not
> save/restore) variant.
>
> When a driver declares as non-atomic via PCM flag, all callbacks
> become sleepable, but this isn't the case for aloop driver.
>
>> I see a potential deadlock in case of free_cable() uses only spin_lock()
>> instead of spin_lock_irqsave().
>> For example the following will be executed:
>>
>> loopback_close()
>> free_cable()
>> spin_lock(&dpcm->cable->lock)
> Which spin_lock() call?  The free_cable() calls spin_lock_irq().
>
>>>> Interrupted by jiffies timer IRQ before calling spin_unlock()
>> loopback_jiffies_timer_function()
>> spin_lock_irqsave(&dpcm->cable->lock)
>>>> DEADLOCK due to dpcm->cable->lock is already locked
>> Do you also see this deadlock or do you see any reason why this could not
>> happen?
> If spin_lock_irq() is used in free_cable(), it must be OK.
>
>
> Takashi
Thanks for the detailed explanation.

@all:
Please simple ignore this patch.

Best regards

Timo

>
>
>> Best regards
>>
>> Timo
>>
>>      thanks,
>>      
>>      Takashi
>>
>>          Signed-off-by: Timo Wischer <[e-mail]>
>>          ---
>>           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
>>
>>

Patch

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) {