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    SubjectRe: [RFC PATCH v9 6/9] media: tegra: Add Tegra210 Video input driver
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    On 4/23/20 5:51 PM, Sowjanya Komatineni wrote:
    >
    > On 4/23/20 5:42 PM, Dmitry Osipenko wrote:
    >> External email: Use caution opening links or attachments
    >>
    >>
    >> 24.04.2020 02:50, Sowjanya Komatineni пишет:
    >>> On 4/23/20 4:25 PM, Dmitry Osipenko wrote:
    >>>> External email: Use caution opening links or attachments
    >>>>
    >>>>
    >>>> 24.04.2020 02:20, Sowjanya Komatineni пишет:
    >>>>> On 4/23/20 4:19 PM, Sowjanya Komatineni wrote:
    >>>>>> On 4/23/20 4:16 PM, Dmitry Osipenko wrote:
    >>>>>>> External email: Use caution opening links or attachments
    >>>>>>>
    >>>>>>>
    >>>>>>> 22.04.2020 09:18, Sowjanya Komatineni пишет:
    >>>>>>>> +static int chan_capture_kthread_start(void *data)
    >>>>>>>> +{
    >>>>>>>> +     struct tegra_vi_channel *chan = data;
    >>>>>>>> +     struct tegra_channel_buffer *buf;
    >>>>>>>> +     int err = 0;
    >>>>>>>> +
    >>>>>>>> +     set_freezable();
    >>>>>>>> +
    >>>>>>>> +     while (1) {
    >>>>>>>> +             try_to_freeze();
    >>>>>>>> +
    >>>>>>>> + wait_event_interruptible(chan->start_wait,
    >>>>>>>> + !list_empty(&chan->capture) ||
    >>>>>>>> + kthread_should_stop());
    >>>>>>>> +
    >>>>>>>> +             if (kthread_should_stop())
    >>>>>>>> +                     break;
    >>>>>>>> +
    >>>>>>>> +             /*
    >>>>>>>> +              * Source is not streaming if error is non-zero.
    >>>>>>>> +              * So, do not dequeue buffers on capture error.
    >>>>>>>> +              */
    >>>>>>>> +             if (err)
    >>>>>>>> +                     continue;
    >>>>>>> This will result in an endless loop, I suppose it wasn't the
    >>>>>>> intention.
    >>>>>> no it will not. on error we report vb2_queue_error which will do
    >>>>>> streaming stop request.
    >>>>>>
    >>>>>> So thread will be stopped on streaming stop request thru kthread
    >>>>>> stop
    >>>>>> signal
    >>>>> To be clear on error it reports vb2 queue error and waits for stop
    >>>>> streaming to happen
    >>>> If thread should exit on error, then it should do it on the actual
    >>>> error. Otherwise it looks very error-prone.
    >>> When v4l2 drivers indicate fatal error through vb2_queue_error, queue
    >>> error flag  is set and wakes up all processes waiting on queue along
    >>> with polling reporting  EPOLLERR and also reporting error for queuing
    >>> and dequeuing buffers. Stream stop will surely happen which stops the
    >>> thread.
    >> This doesn't explain what is the point of continuing to loop instead of
    >> exiting immediately on error.
    >
    > We are using 2 threads and when capture start error happens, we can
    > stop capture_start thread immediately but capture_finish thread will
    > still run for any outstanding buffers.
    >
    > So, as it makes no diff stopping both threads during stream stop which
    > will definitely happen on error and when we don't dequeue buffers
    >
    Also there will be an issue if we break on error immediately during
    stop_streaming -> kthread_stop()

    As stop streaming can happen any time, we do kthread_stop and in case of
    error if we stop thread and on stop streaming kthread_stop might crash
    as kthread_stop can only be called on running thread

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