[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 at 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