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.
I discovered this issue in the allegro-dvt driver [0]. Michael [0] https://lore.kernel.org/linux-media/20190527154557.62278...@litschi.hi.pengutronix.de/ 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(-) -- 2.20.1
