On Mon, Jun 6, 2016 at 4:11 PM, Takashi Iwai <tiwai@xxxxxxx> wrote:
> On Sat, 04 Jun 2016 20:27:50 +0200,
> Dmitry Vyukov wrote:
>>
>> On Sat, Jun 4, 2016 at 8:00 PM, Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>> > Hello,
>> >
>> > The following program triggers use-after-free:
>>
>> Forget to mention that you need to run it in a tight parallel loop. It
>> takes around 5 minutes to reproduce for me.
>
> Hmm, this again is a bug that is difficult to trigger... At least, I
> couldn't reproduce locally. How many processes are you running with
> stress program?
I use a VM with 4 cores and use 20 parallel test processes.
> It seems that there is nothing more than opening /dev/audio and does
> some mmap in the job. Is there any other relevant thing there?
I think poll with timeout is related. It is poll who sets hrtimer, right?
> Also, this assumes that the first sound card is Dummy driver, right?
> Check /proc/asound/cards.
# cat /proc/asound/cards
0 [Dummy ]: Dummy - Dummy
Dummy 1
1 [Loopback ]: Loopback - Loopback
Loopback 1
2 [VirMIDI ]: VirMIDI - VirMIDI
Virtual MIDI Card 1
3 [pcsp ]: PC-Speaker - pcsp
Internal PC-Speaker at port 0x61
4 [Intel ]: HDA-Intel - HDA Intel
HDA Intel at 0xfebf0000 irq 24
> If it's about snd-dummy driver, one blind shot would be a patch like
> below. But even if it would fix, it doesn't explain why it's
> triggered in that way...
>
>
> thanks,
>
> Takashi
>
> ---
> diff --git a/sound/drivers/dummy.c b/sound/drivers/dummy.c
> index c0f8f613f1f1..172dacd925f5 100644
> --- a/sound/drivers/dummy.c
> +++ b/sound/drivers/dummy.c
> @@ -420,6 +420,7 @@ static int dummy_hrtimer_stop(struct snd_pcm_substream *substream)
>
> static inline void dummy_hrtimer_sync(struct dummy_hrtimer_pcm *dpcm)
> {
> + hrtimer_cancel(&dpcm->timer);
> tasklet_kill(&dpcm->tasklet);
> }
>
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