[alsa-devel] [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt()

[alsa-devel] [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt()

[Jia-Ju Bai]

The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger()
may be concurrently executed.

The function snd_cmipci_capture_trigger() calls
snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable
rec->running is written with holding a spinlock cm->reg_lock. But in
snd_cmipci_interrupt(), the identical variable cm->channel[0].running
or cm->channel[1].running is read without holding this spinlock. Thus,
a possible data race may occur.

To fix this data race, in snd_cmipci_interrupt(), the variables
cm->channel[0].running and cm->channel[1].running are read with holding 
the spinlock cm->reg_lock.

This data race is found by the runtime testing of our tool DILP-2.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 sound/pci/cmipci.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c
index dd9d62e2b633..f791152ec48f 100644
--- a/sound/pci/cmipci.c
+++ b/sound/pci/cmipci.c
@@ -1430,7 +1430,7 @@ static int snd_cmipci_capture_spdif_hw_free(struct snd_pcm_substream *subs)
 static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id)
 {
 	struct cmipci *cm = dev_id;
-	unsigned int status, mask = 0;
+	unsigned int run_flag0, run_flag1, status, mask = 0;
 	
 	/* fastpath out, to ease interrupt sharing */
 	status = snd_cmipci_read(cm, CM_REG_INT_STATUS);
@@ -1445,15 +1445,17 @@ static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id)
 		mask |= CM_CH1_INT_EN;
 	snd_cmipci_clear_bit(cm, CM_REG_INT_HLDCLR, mask);
 	snd_cmipci_set_bit(cm, CM_REG_INT_HLDCLR, mask);
+	run_flag0 = cm->channel[0].running;
+	run_flag1 = cm->channel[1].running;
 	spin_unlock(&cm->reg_lock);
 
 	if (cm->rmidi && (status & CM_UARTINT))
 		snd_mpu401_uart_interrupt(irq, cm->rmidi->private_data);
 
 	if (cm->pcm) {
-		if ((status & CM_CHINT0) && cm->channel[0].running)
+		if ((status & CM_CHINT0) && run_flag0)
 			snd_pcm_period_elapsed(cm->channel[0].substream);
-		if ((status & CM_CHINT1) && cm->channel[1].running)
+		if ((status & CM_CHINT1) && run_flag1)
 			snd_pcm_period_elapsed(cm->channel[1].substream);
 	}
 	return IRQ_HANDLED;
-- 
2.17.1

_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [alsa-devel] [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt()

[Takashi Iwai]

On Sat, 11 Jan 2020 17:30:27 +0100,
Jia-Ju Bai wrote:
> 
> The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger()
> may be concurrently executed.
> 
> The function snd_cmipci_capture_trigger() calls
> snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable
> rec->running is written with holding a spinlock cm->reg_lock. But in
> snd_cmipci_interrupt(), the identical variable cm->channel[0].running
> or cm->channel[1].running is read without holding this spinlock. Thus,
> a possible data race may occur.
> 
> To fix this data race, in snd_cmipci_interrupt(), the variables
> cm->channel[0].running and cm->channel[1].running are read with holding 
> the spinlock cm->reg_lock.
> 
> This data race is found by the runtime testing of our tool DILP-2.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>

Thanks for the patch.

That's indeed a kind of race, but this change won't fix anything in
practice, though.  The inconsistent running flag between those places,
there are two cases:

- running became 0 to 1; this cannot happen, as the irq isn't issued
  before the stream gets started

- running became 1 to 0; this means that the stream gets stopped
  between two points, and it's not better to call
  snd_pcm_period_elapsed() for an already stopped stream.


Takashi

> ---
>  sound/pci/cmipci.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/sound/pci/cmipci.c b/sound/pci/cmipci.c
> index dd9d62e2b633..f791152ec48f 100644
> --- a/sound/pci/cmipci.c
> +++ b/sound/pci/cmipci.c
> @@ -1430,7 +1430,7 @@ static int snd_cmipci_capture_spdif_hw_free(struct snd_pcm_substream *subs)
>  static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id)
>  {
>  	struct cmipci *cm = dev_id;
> -	unsigned int status, mask = 0;
> +	unsigned int run_flag0, run_flag1, status, mask = 0;
>  	
>  	/* fastpath out, to ease interrupt sharing */
>  	status = snd_cmipci_read(cm, CM_REG_INT_STATUS);
> @@ -1445,15 +1445,17 @@ static irqreturn_t snd_cmipci_interrupt(int irq, void *dev_id)
>  		mask |= CM_CH1_INT_EN;
>  	snd_cmipci_clear_bit(cm, CM_REG_INT_HLDCLR, mask);
>  	snd_cmipci_set_bit(cm, CM_REG_INT_HLDCLR, mask);
> +	run_flag0 = cm->channel[0].running;
> +	run_flag1 = cm->channel[1].running;
>  	spin_unlock(&cm->reg_lock);
>  
>  	if (cm->rmidi && (status & CM_UARTINT))
>  		snd_mpu401_uart_interrupt(irq, cm->rmidi->private_data);
>  
>  	if (cm->pcm) {
> -		if ((status & CM_CHINT0) && cm->channel[0].running)
> +		if ((status & CM_CHINT0) && run_flag0)
>  			snd_pcm_period_elapsed(cm->channel[0].substream);
> -		if ((status & CM_CHINT1) && cm->channel[1].running)
> +		if ((status & CM_CHINT1) && run_flag1)
>  			snd_pcm_period_elapsed(cm->channel[1].substream);
>  	}
>  	return IRQ_HANDLED;
> -- 
> 2.17.1
> 
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [alsa-devel] [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt()

[Jia-Ju Bai]

On 2020/1/12 16:20, Takashi Iwai wrote:
> On Sat, 11 Jan 2020 17:30:27 +0100,
> Jia-Ju Bai wrote:
>> The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger()
>> may be concurrently executed.
>>
>> The function snd_cmipci_capture_trigger() calls
>> snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable
>> rec->running is written with holding a spinlock cm->reg_lock. But in
>> snd_cmipci_interrupt(), the identical variable cm->channel[0].running
>> or cm->channel[1].running is read without holding this spinlock. Thus,
>> a possible data race may occur.
>>
>> To fix this data race, in snd_cmipci_interrupt(), the variables
>> cm->channel[0].running and cm->channel[1].running are read with holding
>> the spinlock cm->reg_lock.
>>
>> This data race is found by the runtime testing of our tool DILP-2.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> Thanks for the patch.
>
> That's indeed a kind of race, but this change won't fix anything in
> practice, though.  The inconsistent running flag between those places,
> there are two cases:
>
> - running became 0 to 1; this cannot happen, as the irq isn't issued
>    before the stream gets started
>
> - running became 1 to 0; this means that the stream gets stopped
>    between two points, and it's not better to call
>    snd_pcm_period_elapsed() for an already stopped stream.

Thanks for the reply :)

I am not sure to understand your words.

Do you mean that this code should be also protected by the spinlock?
     if (cm->pcm) {
         if ((status & CM_CHINT0) && cm->channel[0].running)
             snd_pcm_period_elapsed(cm->channel[0].substream);
         if ((status & CM_CHINT1) && cm->channel[1].running)
             snd_pcm_period_elapsed(cm->channel[1].substream);
     }


Best wishes,
Jia-Ju Bai
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel

Re: [alsa-devel] [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt()

[Takashi Iwai]

On Mon, 13 Jan 2020 09:20:37 +0100,
Jia-Ju Bai wrote:
> 
> 
> 
> On 2020/1/12 16:20, Takashi Iwai wrote:
> > On Sat, 11 Jan 2020 17:30:27 +0100,
> > Jia-Ju Bai wrote:
> >> The functions snd_cmipci_interrupt() and snd_cmipci_capture_trigger()
> >> may be concurrently executed.
> >>
> >> The function snd_cmipci_capture_trigger() calls
> >> snd_cmipci_pcm_trigger(). In snd_cmipci_pcm_trigger(), the variable
> >> rec->running is written with holding a spinlock cm->reg_lock. But in
> >> snd_cmipci_interrupt(), the identical variable cm->channel[0].running
> >> or cm->channel[1].running is read without holding this spinlock. Thus,
> >> a possible data race may occur.
> >>
> >> To fix this data race, in snd_cmipci_interrupt(), the variables
> >> cm->channel[0].running and cm->channel[1].running are read with holding
> >> the spinlock cm->reg_lock.
> >>
> >> This data race is found by the runtime testing of our tool DILP-2.
> >>
> >> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> > Thanks for the patch.
> >
> > That's indeed a kind of race, but this change won't fix anything in
> > practice, though.  The inconsistent running flag between those places,
> > there are two cases:
> >
> > - running became 0 to 1; this cannot happen, as the irq isn't issued
> >    before the stream gets started
> >
> > - running became 1 to 0; this means that the stream gets stopped
> >    between two points, and it's not better to call
> >    snd_pcm_period_elapsed() for an already stopped stream.
> 
> Thanks for the reply :)
> 
> I am not sure to understand your words.
> 
> Do you mean that this code should be also protected by the spinlock?
>     if (cm->pcm) {
>         if ((status & CM_CHINT0) && cm->channel[0].running)
>             snd_pcm_period_elapsed(cm->channel[0].substream);
>         if ((status & CM_CHINT1) && cm->channel[1].running)
>             snd_pcm_period_elapsed(cm->channel[1].substream);
>     }

No, it can't be protected as it would lead to ABBA deadlock.
That said, it's rather safe to leave the code as is.


thanks,

Takashi
_______________________________________________
Alsa-devel mailing list
Alsa-devel@alsa-project.org
https://mailman.alsa-project.org/mailman/listinfo/alsa-devel