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@xxxxxxxxx>
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
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