Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> writes: > Hi Kevin, > > On Tuesday 06 Dec 2016 08:49:38 Kevin Hilman wrote: >> Laurent Pinchart writes: >> > On Tuesday 29 Nov 2016 15:57:09 Kevin Hilman wrote: >> >> Video capture subdevs may be over I2C and may sleep during xfer, so we >> >> cannot do IRQ-disabled locking when calling the subdev. >> >> >> >> Signed-off-by: Kevin Hilman <khilman@xxxxxxxxxxxx> >> >> --- >> >> drivers/media/platform/davinci/vpif_capture.c | 3 +++ >> >> 1 file changed, 3 insertions(+) >> >> >> >> diff --git a/drivers/media/platform/davinci/vpif_capture.c >> >> b/drivers/media/platform/davinci/vpif_capture.c index >> >> 5104cc0ee40e..9f8f41c0f251 100644 >> >> --- a/drivers/media/platform/davinci/vpif_capture.c >> >> +++ b/drivers/media/platform/davinci/vpif_capture.c >> >> @@ -193,7 +193,10 @@ static int vpif_start_streaming(struct vb2_queue >> >> *vq, unsigned int count) >> >> } >> >> } >> >> >> >> + spin_unlock_irqrestore(&common->irqlock, flags); >> >> ret = v4l2_subdev_call(ch->sd, video, s_stream, 1); >> >> + spin_lock_irqsave(&common->irqlock, flags); >> > >> > I always get anxious when I see a spinlock being released randomly with an >> > operation in the middle of a protected section. Looking at the code it >> > looks like the spinlock is abused here. irqlock should only protect the >> > dma_queue and should thus only be taken around the following code: >> > >> > spin_lock_irqsave(&common->irqlock, flags); >> > /* Get the next frame from the buffer queue */ >> > common->cur_frm = common->next_frm = list_entry(common->dma_queue.next, >> > struct vpif_cap_buffer, list); >> > >> > /* Remove buffer from the buffer queue */ >> > list_del(&common->cur_frm->list); >> > spin_unlock_irqrestore(&common->irqlock, flags); >> >> Yes, that looks correct. Will update. >> >> > The code that is currently protected by the lock in the start and stop >> > streaming functions should be protected by a mutex instead. >> >> I tried taking the mutex here, but lockdep pointed out a deadlock. I >> may not be fully understanding the V4L2 internals here, but it seems >> that the ioctl is already taking a mutex, so taking it again in >> start/stop streaming is a deadlock. Unless you think the locking should >> be nested here, it seems to me that the mutex isn't needed. > > The V4L2 core can lock all ioctls using struct video_device::lock. For buffer- > related ioctls, it can optionally use a separate lock from struct > vb2_queue::lock. See v4l2_ioctl_get_lock() in drivers/media/v4l2-core/v4l2- > ioctl.c. > > The vpif-capture driver sets both the video_device and vb2_queue locks to the > same lock (which would have the same effect as leaving the vb2_queue lock > NULL). All ioctls are thus serialized. You would only need to handle locking > in start_streaming and stop_streaming manually if you didn't rely on the core > serializing the ioctls. OK, thanks for clarifying how that works. Kevin -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
