Le mercredi 14 novembre 2018 à 00:27 +0200, Sakari Ailus a écrit :
> Hi Philipp,
>
> On Tue, Nov 13, 2018 at 04:06:21PM +0100, Philipp Zabel wrote:
> > From: John Sheu <sheu@xxxxxxxxxxxx>
> >
> > Videobuf2 presently does not allow VIDIOC_REQBUFS to destroy outstanding
> > buffers if the queue is of type V4L2_MEMORY_MMAP, and if the buffers are
> > considered "in use". This is different behavior than for other memory
> > types and prevents us from deallocating buffers in following two cases:
> >
> > 1) There are outstanding mmap()ed views on the buffer. However even if
> > we put the buffer in reqbufs(0), there will be remaining references,
> > due to vma .open/close() adjusting vb2 buffer refcount appropriately.
> > This means that the buffer will be in fact freed only when the last
> > mmap()ed view is unmapped.
> >
> > 2) Buffer has been exported as a DMABUF. Refcount of the vb2 buffer
> > is managed properly by VB2 DMABUF ops, i.e. incremented on DMABUF
> > get and decremented on DMABUF release. This means that the buffer
> > will be alive until all importers release it.
> >
> > Considering both cases above, there does not seem to be any need to
> > prevent reqbufs(0) operation, because buffer lifetime is already
> > properly managed by both mmap() and DMABUF code paths. Let's remove it
> > and allow userspace freeing the queue (and potentially allocating a new
> > one) even though old buffers might be still in processing.
> >
> > To let userspace know that the kernel now supports orphaning buffers
> > that are still in use, add a new V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS
> > to be set by reqbufs and create_bufs.
> >
> > Signed-off-by: John Sheu <sheu@xxxxxxxxxxxx>
> > Reviewed-by: Pawel Osciak <posciak@xxxxxxxxxxxx>
> > Reviewed-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > Signed-off-by: Tomasz Figa <tfiga@xxxxxxxxxxxx>
> > [p.zabel@xxxxxxxxxxxxxx: moved __vb2_queue_cancel out of the mmap_lock
> > and added V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS]
> > Signed-off-by: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx>
>
> This lets the user to allocate lots of mmap'ed buffers that are pinned in
> physical memory. Considering that we don't really have a proper mechanism
> to limit that anyway,
It's currently limited to 32 buffers. It's not worst then DRM dumb
buffers which will let you allocate as much as you want.
>
> Acked-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
>
> That said, the patch must be accompanied by the documentation change in
> Documentation/media/uapi/v4l/vidioc-reqbufs.rst .
>
> I wonder what Hans thinks.
>
> > ---
> > .../media/common/videobuf2/videobuf2-core.c | 26 +------------------
> > .../media/common/videobuf2/videobuf2-v4l2.c | 2 +-
> > include/uapi/linux/videodev2.h | 1 +
> > 3 files changed, 3 insertions(+), 26 deletions(-)
> >
> > diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
> > index 975ff5669f72..608459450c1e 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-core.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-core.c
> > @@ -553,20 +553,6 @@ bool vb2_buffer_in_use(struct vb2_queue *q, struct vb2_buffer *vb)
> > }
> > EXPORT_SYMBOL(vb2_buffer_in_use);
> >
> > -/*
> > - * __buffers_in_use() - return true if any buffers on the queue are in use and
> > - * the queue cannot be freed (by the means of REQBUFS(0)) call
> > - */
> > -static bool __buffers_in_use(struct vb2_queue *q)
> > -{
> > - unsigned int buffer;
> > - for (buffer = 0; buffer < q->num_buffers; ++buffer) {
> > - if (vb2_buffer_in_use(q, q->bufs[buffer]))
> > - return true;
> > - }
> > - return false;
> > -}
> > -
> > void vb2_core_querybuf(struct vb2_queue *q, unsigned int index, void *pb)
> > {
> > call_void_bufop(q, fill_user_buffer, q->bufs[index], pb);
> > @@ -674,23 +660,13 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
> >
> > if (*count == 0 || q->num_buffers != 0 ||
> > (q->memory != VB2_MEMORY_UNKNOWN && q->memory != memory)) {
> > - /*
> > - * We already have buffers allocated, so first check if they
> > - * are not in use and can be freed.
> > - */
> > - mutex_lock(&q->mmap_lock);
> > - if (q->memory == VB2_MEMORY_MMAP && __buffers_in_use(q)) {
> > - mutex_unlock(&q->mmap_lock);
> > - dprintk(1, "memory in use, cannot free\n");
> > - return -EBUSY;
> > - }
> > -
> > /*
> > * Call queue_cancel to clean up any buffers in the
> > * QUEUED state which is possible if buffers were prepared or
> > * queued without ever calling STREAMON.
> > */
> > __vb2_queue_cancel(q);
> > + mutex_lock(&q->mmap_lock);
> > ret = __vb2_queue_free(q, q->num_buffers);
> > mutex_unlock(&q->mmap_lock);
> > if (ret)
> > diff --git a/drivers/media/common/videobuf2/videobuf2-v4l2.c b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > index a17033ab2c22..f02d452ceeb9 100644
> > --- a/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > +++ b/drivers/media/common/videobuf2/videobuf2-v4l2.c
> > @@ -624,7 +624,7 @@ EXPORT_SYMBOL(vb2_querybuf);
> >
> > static void fill_buf_caps(struct vb2_queue *q, u32 *caps)
> > {
> > - *caps = 0;
> > + *caps = V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS;
> > if (q->io_modes & VB2_MMAP)
> > *caps |= V4L2_BUF_CAP_SUPPORTS_MMAP;
> > if (q->io_modes & VB2_USERPTR)
> > diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h
> > index c8e8ff810190..2a223835214c 100644
> > --- a/include/uapi/linux/videodev2.h
> > +++ b/include/uapi/linux/videodev2.h
> > @@ -879,6 +879,7 @@ struct v4l2_requestbuffers {
> > #define V4L2_BUF_CAP_SUPPORTS_USERPTR (1 << 1)
> > #define V4L2_BUF_CAP_SUPPORTS_DMABUF (1 << 2)
> > #define V4L2_BUF_CAP_SUPPORTS_REQUESTS (1 << 3)
> > +#define V4L2_BUF_CAP_SUPPORTS_ORPHANED_BUFS (1 << 4)
> >
> > /**
> > * struct v4l2_plane - plane info for multi-planar buffers
