do_poll()/do_select() seem to set the _qproc member of poll_table to NULL the first time they are called on a given table, making subsequent calls of poll_wait() on that table no-ops. This is a problem for vb2 which calls poll_wait() on the V4L2 queues' waitqueues only when a queue-related event is requested, which may not necessarily be the case during the first poll. Fix this by making the call to poll_wait() happen first thing and unconditionally in vb2_core_poll(). Signed-off-by: Alexandre Courbot <gnurou@xxxxxxxxx> --- drivers/media/common/videobuf2/videobuf2-core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c index 4eab6d81cce1..ef06f90f5c6b 100644 --- a/drivers/media/common/videobuf2/videobuf2-core.c +++ b/drivers/media/common/videobuf2/videobuf2-core.c @@ -2363,13 +2363,20 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file, struct vb2_buffer *vb = NULL; unsigned long flags; + /* + * poll_wait() MUST be called on the first invocation on all the + * potential queues of interest, even if we are not interested in their + * events during this first call. Failure to do so will result in + * queue's events to be ignored because the poll_table won't be capable + * of adding new wait queues thereafter. + */ + poll_wait(file, &q->done_wq, wait); + if (!q->is_output && !(req_events & (EPOLLIN | EPOLLRDNORM))) return 0; if (q->is_output && !(req_events & (EPOLLOUT | EPOLLWRNORM))) return 0; - poll_wait(file, &q->done_wq, wait); - /* * Start file I/O emulator only if streaming API has not been used yet. */ -- 2.29.2
