| Message ID | 20161129235712.29846-2-khilman@baylibre.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
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@baylibre.com> > --- > 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); The code that is currently protected by the lock in the start and stop streaming functions should be protected by a mutex instead. > + > if (ret && ret != -ENOIOCTLCMD && ret != -ENODEV) { > vpif_dbg(1, debug, "stream on failed in subdev\n"); > goto err;
Laurent Pinchart <laurent.pinchart@ideasonboard.com> 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@baylibre.com> >> --- >> 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
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@baylibre.com> > >> --- > >> 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.
Laurent Pinchart <laurent.pinchart@ideasonboard.com> 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@baylibre.com> >> >> --- >> >> 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
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); + if (ret && ret != -ENOIOCTLCMD && ret != -ENODEV) { vpif_dbg(1, debug, "stream on failed in subdev\n"); goto err;
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@baylibre.com> --- drivers/media/platform/davinci/vpif_capture.c | 3 +++ 1 file changed, 3 insertions(+)