A user can close the codec while keeping references to some of the
capture buffers. When the codec is closed, the structure that keeps
the contexts, state and the driver file descriptor is freed.
Since access to some of the elements in that structure is required to
properly release the memory during the buffer unref callbacks, the
following commit makes sure the unref callback accesses valid memory.
This commit was tested with valgrind:
$ valgrind ffmpeg_g -report -threads 1 -v 55 -y -c:v h264_v4l2m2m \
-i video.h264 -an -frames:v 100 -f null -
---
libavcodec/v4l2_buffers.c | 17 ++++++++++++++++-
libavcodec/v4l2_buffers.h | 6 ++++++
libavcodec/v4l2_m2m.c | 29 ++++++++++++++++++++++++-----
libavcodec/v4l2_m2m_dec.c | 2 +-
4 files changed, 47 insertions(+), 7 deletions(-)
diff --git a/libavcodec/v4l2_buffers.c b/libavcodec/v4l2_buffers.c
index ba70c5d..80e65ca 100644
--- a/libavcodec/v4l2_buffers.c
+++ b/libavcodec/v4l2_buffers.c
@@ -205,9 +205,24 @@ static enum AVColorTransferCharacteristic
v4l2_get_color_trc(V4L2Buffer *buf)
static void v4l2_free_buffer(void *opaque, uint8_t *unused)
{
V4L2Buffer* avbuf = opaque;
- V4L2m2mContext *s = buf_to_m2mctx(avbuf);
+ V4L2m2mContext *s = avbuf->m2m ? avbuf->m2m : buf_to_m2mctx(avbuf);
atomic_fetch_sub_explicit(&s->refcount, 1, memory_order_acq_rel);
+
+ if (avbuf->m2m) {
+ if (!atomic_load(&s->refcount)) {
+ /* unmmap and free the associated buffers */
+ ff_v4l2_context_release(&s->capture);
+
+ /* close the v4l2 driver */
+ close(s->fd);
+
+ /* release the duplicated m2m context */
+ av_freep(&s);
+ }
+ return;
+ }
+
if (s->reinit) {
if (!atomic_load(&s->refcount))
sem_post(&s->refsync);
diff --git a/libavcodec/v4l2_buffers.h b/libavcodec/v4l2_buffers.h
index e28a4a6..d774480 100644
--- a/libavcodec/v4l2_buffers.h
+++ b/libavcodec/v4l2_buffers.h
@@ -41,6 +41,12 @@ typedef struct V4L2Buffer {
/* each buffer needs to have a reference to its context */
struct V4L2Context *context;
+ /* when the codec is closed while the user has buffer references we
+ * still need access to context data (this is a pointer to a duplicated
+ * m2m context created during the codec close function).
+ */
+ struct V4L2m2mContext *m2m;
+
/* keep track of the mmap address and mmap length */
struct V4L2Plane_info {
int bytesperline;
diff --git a/libavcodec/v4l2_m2m.c b/libavcodec/v4l2_m2m.c
index 1d7a852..91b1bbb 100644
--- a/libavcodec/v4l2_m2m.c
+++ b/libavcodec/v4l2_m2m.c
@@ -313,8 +313,8 @@ error:
int ff_v4l2_m2m_codec_end(AVCodecContext *avctx)
{
- V4L2m2mContext* s = avctx->priv_data;
- int ret;
+ V4L2m2mContext *m2m, *s = avctx->priv_data;
+ int i, ret;
ret = ff_v4l2_context_set_status(&s->output, VIDIOC_STREAMOFF);
if (ret)
@@ -325,12 +325,31 @@ int ff_v4l2_m2m_codec_end(AVCodecContext *avctx)
av_log(avctx, AV_LOG_ERROR, "VIDIOC_STREAMOFF %s\n", s->capture.name);
ff_v4l2_context_release(&s->output);
+ sem_destroy(&s->refsync);
- if (atomic_load(&s->refcount))
- av_log(avctx, AV_LOG_ERROR, "ff_v4l2m2m_codec_end leaving pending
buffers\n");
+ if (atomic_load(&s->refcount)) {
+ av_log(avctx, AV_LOG_DEBUG, "ff_v4l2m2m_codec_end, referenced buffers %d\n",
atomic_load(&s->refcount));
+
+ /* We are about to free the private data while the user still has
references to the buffers.
+ * This means that when the user releases those buffers, the
v4l2_free_buffer callback will be pointing to free'd memory.
+ * Duplicate the m2m context and update the buffers.
+ */
+ m2m = av_mallocz(sizeof(*m2m));
+ if (m2m) {
+ memcpy(m2m, s, sizeof(V4L2m2mContext));
+ for (i = 0; i < s->capture.num_buffers; i++)
+ s->capture.buffers[i].m2m = m2m;
+
+ return 0;
+ }
+
+ /* on ENOMEM let's at least close the v4l2 driver and release the
capture memory
+ * so the driver is left in a healthy state.
+ */
+ av_log(avctx, AV_LOG_ERROR, "ff_v4l2m2m_codec_end, referenced buffers not
accessible\n");
+ }
