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