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