V4L/DVB (7493): videobuf: Avoid deadlock with QBUF and bring up to spec for empty queue
Add a waitqueue to wait on when there are no buffers in the buffer queue.
DQBUF waits on this queue without holding vb_lock to allow a QBUF to happen.
Once a buffer has been queued we recheck that the queue is still streaming and
wait on the new buffer's waitqueue while holding the vb_lock. The driver
should come along in a timely manner and put the buffer into its next state
finishing the DQBUF.
By implementing this waitqueue it also brings the videobuf DQBUF up to spec and
it now blocks on O_NONBLOCK even when no buffers have been queued via QBUF:
"By default VIDIOC_DQBUF blocks when no buffer is in the outgoing queue."
- V4L2 spec
Signed-off-by: Brandon Philips <bphilips@suse.de>
CC: Trent Piepho <xyzzy@speakeasy.org>
CC: Carl Karsten <carl@personnelware.com>
CC: Jonathan Corbet <corbet@lwn.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
diff --git a/drivers/media/video/videobuf-core.c b/drivers/media/video/videobuf-core.c
index 1ba3aaa..3ab5560 100644
--- a/drivers/media/video/videobuf-core.c
+++ b/drivers/media/video/videobuf-core.c
@@ -141,6 +141,7 @@
BUG_ON(!q->int_ops);
mutex_init(&q->vb_lock);
+ init_waitqueue_head(&q->wait);
INIT_LIST_HEAD(&q->stream);
}
@@ -188,6 +189,10 @@
unsigned long flags = 0;
int i;
+ q->streaming = 0;
+ q->reading = 0;
+ wake_up_interruptible_sync(&q->wait);
+
/* remove queued buffers from list */
if (q->irqlock)
spin_lock_irqsave(q->irqlock, flags);
@@ -565,6 +570,7 @@
}
dprintk(1, "qbuf: succeded\n");
retval = 0;
+ wake_up_interruptible_sync(&q->wait);
done:
mutex_unlock(&q->vb_lock);
@@ -575,37 +581,88 @@
return retval;
}
+
+/* Locking: Caller holds q->vb_lock */
+static int stream_next_buffer_check_queue(struct videobuf_queue *q, int noblock)
+{
+ int retval;
+
+checks:
+ if (!q->streaming) {
+ dprintk(1, "next_buffer: Not streaming\n");
+ retval = -EINVAL;
+ goto done;
+ }
+
+ if (list_empty(&q->stream)) {
+ if (noblock) {
+ retval = -EAGAIN;
+ dprintk(2, "next_buffer: no buffers to dequeue\n");
+ goto done;
+ } else {
+ dprintk(2, "next_buffer: waiting on buffer\n");
+
+ /* Drop lock to avoid deadlock with qbuf */
+ mutex_unlock(&q->vb_lock);
+
+ /* Checking list_empty and streaming is safe without
+ * locks because we goto checks to validate while
+ * holding locks before proceeding */
+ retval = wait_event_interruptible(q->wait,
+ !list_empty(&q->stream) || !q->streaming);
+ mutex_lock(&q->vb_lock);
+
+ if (retval)
+ goto done;
+
+ goto checks;
+ }
+ }
+
+ retval = 0;
+
+done:
+ return retval;
+}
+
+
+/* Locking: Caller holds q->vb_lock */
+static int stream_next_buffer(struct videobuf_queue *q,
+ struct videobuf_buffer **vb, int nonblocking)
+{
+ int retval;
+ struct videobuf_buffer *buf = NULL;
+
+ retval = stream_next_buffer_check_queue(q, nonblocking);
+ if (retval)
+ goto done;
+
+ buf = list_entry(q->stream.next, struct videobuf_buffer, stream);
+ retval = videobuf_waiton(buf, nonblocking, 1);
+ if (retval < 0)
+ goto done;
+
+ *vb = buf;
+done:
+ return retval;
+}
+
int videobuf_dqbuf(struct videobuf_queue *q,
struct v4l2_buffer *b, int nonblocking)
{
- struct videobuf_buffer *buf;
+ struct videobuf_buffer *buf = NULL;
int retval;
MAGIC_CHECK(q->int_ops->magic, MAGIC_QTYPE_OPS);
mutex_lock(&q->vb_lock);
- retval = -EBUSY;
- if (q->reading) {
- dprintk(1, "dqbuf: Reading running...\n");
- goto done;
- }
- retval = -EINVAL;
- if (b->type != q->type) {
- dprintk(1, "dqbuf: Wrong type.\n");
- goto done;
- }
- if (list_empty(&q->stream)) {
- dprintk(1, "dqbuf: stream running\n");
- goto done;
- }
- buf = list_entry(q->stream.next, struct videobuf_buffer, stream);
- mutex_unlock(&q->vb_lock);
- retval = videobuf_waiton(buf, nonblocking, 1);
- mutex_lock(&q->vb_lock);
+
+ retval = stream_next_buffer(q, &buf, nonblocking);
if (retval < 0) {
- dprintk(1, "dqbuf: waiton returned %d\n", retval);
+ dprintk(1, "dqbuf: next_buffer error: %i\n", retval);
goto done;
}
+
switch (buf->state) {
case VIDEOBUF_ERROR:
dprintk(1, "dqbuf: state is error\n");
@@ -654,6 +711,7 @@
if (q->irqlock)
spin_unlock_irqrestore(q->irqlock, flags);
+ wake_up_interruptible_sync(&q->wait);
done:
mutex_unlock(&q->vb_lock);
return retval;
@@ -666,7 +724,6 @@
return -EINVAL;
videobuf_queue_cancel(q);
- q->streaming = 0;
return 0;
}
@@ -869,7 +926,6 @@
q->bufs[i] = NULL;
}
q->read_buf = NULL;
- q->reading = 0;
}