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media: videobuf2: always call poll_wait() on queues 

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@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Alexandre Courbot 2020-12-01 13:44:41 +01:00 committed by Mauro Carvalho Chehab
parent a45c39b829
commit 575c52cc4c
1 changed files with 9 additions and 2 deletions
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11
drivers/media/common/videobuf2/videobuf2-core.c
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@ -2374,13 +2374,20 @@ __poll_t vb2_core_poll(struct vb2_queue *q, struct file *file,
struct vb2_buffer *vb = NULL; struct vb2_buffer *vb = NULL;
unsigned long flags; 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))) if (!q->is_output && !(req_events & (EPOLLIN | EPOLLRDNORM)))
return 0; return 0;
if (q->is_output && !(req_events & (EPOLLOUT | EPOLLWRNORM))) if (q->is_output && !(req_events & (EPOLLOUT | EPOLLWRNORM)))
return 0; return 0;
poll_wait(file, &q->done_wq, wait);
/* /*
* Start file I/O emulator only if streaming API has not been used yet. * Start file I/O emulator only if streaming API has not been used yet.
*/ */