Messages in this thread | | | Subject | Re: [PATCH] ALSA: cmipci: Fix possible a data race in snd_cmipci_interrupt() | From | Jia-Ju Bai <> | Date | Mon, 13 Jan 2020 16:20:37 +0800 |
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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); }
Best wishes, Jia-Ju Bai
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