Closed sanbrother closed 1 year ago
i just ran into the same issue.
running a git bisect
between v0.12.7
and current HEAD
also shows that the mentioned commit is the culprit.
i then tested with a revert-commit and the problem goes away.
this is the revert-patch:
diff --git a/v4l2loopback.c b/v4l2loopback.c
index 2ab1f76..2514f09 100644
--- a/v4l2loopback.c
+++ b/v4l2loopback.c
@@ -92,17 +92,6 @@ MODULE_LICENSE("GPL");
} \
} while (0)
-/* TODO: Make sure that function is never interrupted. */
-static inline int mod_inc(int *number, int mod)
-{
- int result;
- result = (*number + 1) % mod;
- if (unlikely(result < 0))
- result += mod;
- *number = result;
- return result;
-}
-
static inline void v4l2l_get_timestamp(struct v4l2_buffer *b)
{
/* ktime_get_ts is considered deprecated, so use ktime_get_ts64 if possible */
@@ -1424,8 +1413,9 @@ static int vidioc_reqbufs(struct file *file, void *fh,
i = dev->write_position;
list_for_each_entry(pos, &dev->outbufs_list,
list_head) {
- dev->bufpos2index[mod_inc(&i, b->count)] =
+ dev->bufpos2index[i % b->count] =
pos->buffer.index;
+ ++i;
}
}
@@ -1489,9 +1479,10 @@ static void buffer_written(struct v4l2_loopback_device *dev,
del_timer_sync(&dev->timeout_timer);
spin_lock_bh(&dev->lock);
- dev->bufpos2index[mod_inc(&dev->write_position, dev->used_buffers)] =
+ dev->bufpos2index[dev->write_position % dev->used_buffers] =
buf->buffer.index;
list_move_tail(&buf->list_head, &dev->outbufs_list);
+ ++dev->write_position;
dev->reread_count = 0;
check_timers(dev);
@@ -1586,7 +1577,8 @@ static int get_capture_buffer(struct file *file)
if (dev->write_position >
opener->read_position + dev->used_buffers)
opener->read_position = dev->write_position - 1;
- pos = mod_inc(&opener->read_position, dev->used_buffers);
+ pos = opener->read_position % dev->used_buffers;
+ ++opener->read_position;
}
timeout_happened = dev->timeout_happened;
dev->timeout_happened = 0;
i just ran into the same issue. running a
git bisect
betweenv0.12.7
and currentHEAD
also shows that the mentioned commit is the culprit. i then tested with a revert-commit and the problem goes away.
It seems that, the base code depends heavily on read_position and write_position. If modulo operation applied on the two variables, it is hard to judge if (write_position > read_position) is true. So, as you see, my patch just increase the input number, but returns a modulo value. But it is strange to read the code.
Environment
v4l2loopback
version: upstream commit fb410fc7af40e972058809a191fae9517b9313afProblem:
gst-launch-1.0 stops at first frame, seems freezed.
Steps to reproduce:
Relevant Code:
I'm sure, the commit https://github.com/umlaeute/v4l2loopback/commit/ff4e9ee3510109333ace2645ff5b7d1f7edb36d9 introduced a bug.
Here is my patch, strange, but works. As far as I understand, write_position and read_position should not be applied modulo operation.