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Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver
From:   Sowjanya Komatineni <skomatineni@nvidia.com>
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On 4/6/20 1:38 PM, Sowjanya Komatineni wrote:
>
> On 4/6/20 1:37 PM, Dmitry Osipenko wrote:
>> External email: Use caution opening links or attachments
>>
>>
>> 06.04.2020 23:20, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>> On 4/6/20 1:02 PM, Dmitry Osipenko wrote:
>>>> External email: Use caution opening links or attachments
>>>>
>>>>
>>>> 04.04.2020 04:25, Sowjanya Komatineni =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>> ...
>>>>> +static int chan_capture_kthread_start(void *data)
>>>>> +{
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_vi_channel *chan =3D data;
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 struct tegra_channel_buffer *buf;
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 int err =3D 0;
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 int caps_inflight;
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 set_freezable();
>>>>> +
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 while (1) {
>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0 try_to_freeze();
>>>>> +
>>>>> + wait_event_interruptible(chan->start_wait,
>>>>> + !list_empty(&chan->capture) ||
>>>>> + kthread_should_stop());
>>>> Is it really okay that list_empty() isn't protected with a lock?

wakeup on thread happens either when buffer is moved to capture list or=20
on stop signaling event.

So in this specific case we may not need to check for lock on capture=20
list as if wakeup happens from start wait queue, then buffer is already=20
moved to capture list by then.

>>>>
>>>> Why wait_event is "interruptible"?
>>> To allow it to sleep until wakeup on thread it to avoid constant
>>> checking for condition even when no buffers are ready, basically to
>>> prevent blocking.
>> So the "interrupt" is for getting event about kthread_should_stop(),
>> correct?
> also to prevent blocking and to let is sleep and wakeup based on wait=20
> queue to evaluate condition to proceed with the task
>>