Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> writes: > Hi Kevin, > > Thank you for the patch. > > 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. Kevin -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
