The vb2_fop_poll() implementation tries to be clever on whether it needs
to lock the queue mutex by checking whether polling might start fileio.
The test requires reading the q->num_buffer field, which is racy if we
don't hold the queue mutex in the first place.
Remove the extra cleverness and just lock the mutex.
Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Acked-by: Hans Verkuil <hans.verkuil@xxxxxxxxx>
---
drivers/media/v4l2-core/videobuf2-core.c | 27 ++++++++-------------------
1 file changed, 8 insertions(+), 19 deletions(-)
diff --git a/drivers/media/v4l2-core/videobuf2-core.c b/drivers/media/v4l2-core/videobuf2-core.c
index 7aed8f2..2685670 100644
--- a/drivers/media/v4l2-core/videobuf2-core.c
+++ b/drivers/media/v4l2-core/videobuf2-core.c
@@ -3459,27 +3459,16 @@ unsigned int vb2_fop_poll(struct file *file, poll_table *wait)
struct video_device *vdev = video_devdata(file);
struct vb2_queue *q = vdev->queue;
struct mutex *lock = q->lock ? q->lock : vdev->lock;
- unsigned long req_events = poll_requested_events(wait);
unsigned res;
void *fileio;
- bool must_lock = false;
-
- /* Try to be smart: only lock if polling might start fileio,
- otherwise locking will only introduce unwanted delays. */
- if (q->num_buffers == 0 && !vb2_fileio_is_active(q)) {
- if (!V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_READ) &&
- (req_events & (POLLIN | POLLRDNORM)))
- must_lock = true;
- else if (V4L2_TYPE_IS_OUTPUT(q->type) && (q->io_modes & VB2_WRITE) &&
- (req_events & (POLLOUT | POLLWRNORM)))
- must_lock = true;
- }
- /* If locking is needed, but this helper doesn't know how, then you
- shouldn't be using this helper but you should write your own. */
- WARN_ON(must_lock && !lock);
+ /*
+ * If this helper doesn't know how to lock, then you shouldn't be using
+ * it but you should write your own.
+ */
+ WARN_ON(!lock);
- if (must_lock && lock && mutex_lock_interruptible(lock))
+ if (lock && mutex_lock_interruptible(lock))
return POLLERR;
fileio = q->fileio;
@@ -3487,9 +3476,9 @@ unsigned int vb2_fop_poll(struct file *file, poll_table *wait)
res = vb2_poll(vdev->queue, file, wait);
/* If fileio was started, then we have a new queue owner. */
- if (must_lock && !fileio && q->fileio)
+ if (!fileio && q->fileio)
q->owner = file->private_data;
- if (must_lock && lock)
+ if (lock)
mutex_unlock(lock);
return res;
}
--
2.0.4
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