Hi Alexandre,
On Tue, 25 Aug 2020 at 11:56, Alexandre Courbot <gnurou@xxxxxxxxx> wrote:
>
> If poll() is called on a m2m device with the EPOLLOUT event after the
> last buffer of the CAPTURE queue is dequeued, any buffer available on
> OUTPUT queue will never be signaled because v4l2_m2m_poll_for_data()
> starts by checking whether dst_q->last_buffer_dequeued is set and
> returns EPOLLIN in this case, without looking at the state of the OUTPUT
> queue.
>
> Fix this by checking the state of the OUTPUT queue before considering
> that early-return case.
>
> This also has the side-effect of bringing the two blocks of code dealing
> with the CAPTURE queue next to one another, and saves us one spin
> lock/unlock cycle, for what it's worth.
>
> Signed-off-by: Alexandre Courbot <gnurou@xxxxxxxxx>
Change looks good to me.
Reviewed-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxx>
Do you think it qualifies for -stable? The issue has been
here since the dawn of time.
Thanks,
Ezequiel
> ---
> drivers/media/v4l2-core/v4l2-mem2mem.c | 23 +++++++++++------------
> 1 file changed, 11 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> index 95a8f2dc5341d..0d0192119af20 100644
> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> @@ -862,6 +862,15 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
> list_empty(&dst_q->queued_list)))
> return EPOLLERR;
>
> + spin_lock_irqsave(&src_q->done_lock, flags);
> + if (!list_empty(&src_q->done_list))
> + src_vb = list_first_entry(&src_q->done_list, struct vb2_buffer,
> + done_entry);
> + if (src_vb && (src_vb->state == VB2_BUF_STATE_DONE
> + || src_vb->state == VB2_BUF_STATE_ERROR))
> + rc |= EPOLLOUT | EPOLLWRNORM;
> + spin_unlock_irqrestore(&src_q->done_lock, flags);
> +
> spin_lock_irqsave(&dst_q->done_lock, flags);
> if (list_empty(&dst_q->done_list)) {
> /*
> @@ -870,21 +879,11 @@ static __poll_t v4l2_m2m_poll_for_data(struct file *file,
> */
> if (dst_q->last_buffer_dequeued) {
> spin_unlock_irqrestore(&dst_q->done_lock, flags);
> - return EPOLLIN | EPOLLRDNORM;
> + rc |= EPOLLIN | EPOLLRDNORM;
> + return rc;
> }
> }
> - spin_unlock_irqrestore(&dst_q->done_lock, flags);
>
> - spin_lock_irqsave(&src_q->done_lock, flags);
> - if (!list_empty(&src_q->done_list))
> - src_vb = list_first_entry(&src_q->done_list, struct vb2_buffer,
> - done_entry);
> - if (src_vb && (src_vb->state == VB2_BUF_STATE_DONE
> - || src_vb->state == VB2_BUF_STATE_ERROR))
> - rc |= EPOLLOUT | EPOLLWRNORM;
> - spin_unlock_irqrestore(&src_q->done_lock, flags);
> -
> - spin_lock_irqsave(&dst_q->done_lock, flags);
> if (!list_empty(&dst_q->done_list))
> dst_vb = list_first_entry(&dst_q->done_list, struct vb2_buffer,
> done_entry);
> --
> 2.28.0
>
