[v2,0/2] vb2: check for events before checking for buffers

Message

Michael Tretter June 27, 2019, 12:44 p.m. UTC

The patches fix a race condition in the poll functions of v4l2 devices.

Whenever a driver returns a buffer with the V4L2_BUF_FLAG_LAST flag set, it
must also return a V4L2_EVENT_EOS. Checking for events before checking for
buffers creates a race condition where drivers can return the buffer and event
between the checks and thus only signal the buffer without the event.
Reordering the checks avoids the race condition.

As suggested by Hans, I renamed __v4l2_m2m_poll() to v4l2_m2m_poll_for_data()
in patch 2/2.

Michael

Changelog:

v1 -> v2:
- rename __v4l2_m2m_poll() to v4l2_m2m_poll_for_data

Michael Tretter (2):
  media: vb2: reorder checks in vb2_poll()
  media: v4l2-mem2mem: reorder checks in v4l2_m2m_poll()

 .../media/common/videobuf2/videobuf2-v4l2.c   |  8 ++--
 drivers/media/v4l2-core/v4l2-mem2mem.c        | 47 +++++++++++--------
 2 files changed, 32 insertions(+), 23 deletions(-)