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 <[email protected]>
---
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
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 <[email protected]>
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
>
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 <[email protected]>
> 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
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 <[email protected]>
> > 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