In blocking mode, if there are no buffers available the DQBUF will block
waiting for a QBUF to be called but it will block holding the streaming
lock which will prevent any QBUF from happening, causing a deadlock.
Can be tested with: v4l2grab -t -b -s 2000
Signed-off-by: Thiago Santos <ts.santos@xxxxxxxxxxxxxxxx>
---
lib/libv4l2/libv4l2-priv.h | 1 +
lib/libv4l2/libv4l2.c | 13 ++++++++++++-
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/lib/libv4l2/libv4l2-priv.h b/lib/libv4l2/libv4l2-priv.h
index 585273c..ff4c8d2 100644
--- a/lib/libv4l2/libv4l2-priv.h
+++ b/lib/libv4l2/libv4l2-priv.h
@@ -92,6 +92,7 @@ struct v4l2_dev_info {
unsigned char *frame_pointers[V4L2_MAX_NO_FRAMES];
int frame_sizes[V4L2_MAX_NO_FRAMES];
int frame_queued; /* 1 status bit per frame */
+ int frame_info_generation;
/* mapping tracking of our fake (converting mmap) frame buffers */
unsigned char frame_map_count[V4L2_MAX_NO_FRAMES];
/* buffer when doing conversion and using read() for read() */
diff --git a/lib/libv4l2/libv4l2.c b/lib/libv4l2/libv4l2.c
index c4d69f7..1dcf34d 100644
--- a/lib/libv4l2/libv4l2.c
+++ b/lib/libv4l2/libv4l2.c
@@ -282,7 +282,7 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
unsigned char *dest, int dest_size)
{
const int max_tries = V4L2_IGNORE_FIRST_FRAME_ERRORS + 1;
- int result, tries = max_tries;
+ int result, tries = max_tries, frame_info_gen;
/* Make sure we have the real v4l2 buffers mapped */
result = v4l2_map_buffers(index);
@@ -290,9 +290,12 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
return result;
do {
+ frame_info_gen = devices[index].frame_info_generation;
+ pthread_mutex_unlock(&devices[index].stream_lock);
result = devices[index].dev_ops->ioctl(
devices[index].dev_ops_priv,
devices[index].fd, VIDIOC_DQBUF, buf);
+ pthread_mutex_lock(&devices[index].stream_lock);
if (result) {
if (errno != EAGAIN) {
int saved_err = errno;
@@ -305,6 +308,11 @@ static int v4l2_dequeue_and_convert(int index, struct v4l2_buffer *buf,
devices[index].frame_queued &= ~(1 << buf->index);
+ if (frame_info_gen != devices[index].frame_info_generation) {
+ errno = -EINVAL;
+ return -1;
+ }
+
result = v4lconvert_convert(devices[index].convert,
&devices[index].src_fmt, &devices[index].dest_fmt,
devices[index].frame_pointers[buf->index],
@@ -839,6 +847,7 @@ int v4l2_dup(int fd)
static int v4l2_check_buffer_change_ok(int index)
{
+ devices[index].frame_info_generation++;
v4l2_unmap_buffers(index);
/* Check if the app itself still is using the stream */
@@ -1294,9 +1303,11 @@ no_capture_request:
}
if (!v4l2_needs_conversion(index)) {
+ pthread_mutex_unlock(&devices[index].stream_lock);
result = devices[index].dev_ops->ioctl(
devices[index].dev_ops_priv,
fd, VIDIOC_DQBUF, buf);
+ pthread_mutex_lock(&devices[index].stream_lock);
if (result) {
saved_err = errno;
V4L2_PERROR("dequeuing buf");
--
2.0.0
--
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