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fix: serialize concurrent GBM buffer allocation in dup_gst_memory_as_dmabuf to prevent SIGSEGV in libgallium with multiple concurrent video pipelines #522

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fix: serialize concurrent GBM buffer allocation in dup_gst_memory_as_dmabuf to prevent SIGSEGV in libgallium with multiple concurrent video pipelines #522

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17 changes: 15 additions & 2 deletions src/plugins/gstreamer_video_player/frame.c
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Original file line number Diff line number Diff line change
Expand Up @@ -27,6 +27,15 @@
#define DRM_FOURCC_FORMAT "c%c%c%c"
#define DRM_FOURCC_ARGS(format) (format) & 0xFF, ((format) >> 8) & 0xFF, ((format) >> 16) & 0xFF, ((format) >> 24) & 0xFF

// Serializes access to gbm_bo_create/gbm_bo_map/gbm_bo_get_fd.
// Mesa's Gallium GBM/DRI backend is not safe against concurrent calls
// into the same gbm_device from multiple threads -- without this lock,
// concurrent video zones each running their own GStreamer pipeline thread
// can segfault inside libgallium when calling dup_gst_memory_as_dmabuf()
// simultaneously (observed via gdb, SIGSEGV in libgallium.so called from
// frame.c, thread = a GStreamer "multiqueueN:src" worker thread).
static pthread_mutex_t gbm_lock = PTHREAD_MUTEX_INITIALIZER;

struct video_frame {
GstSample *sample;

Expand Down Expand Up @@ -415,10 +424,12 @@ UNUSED int dup_gst_memory_as_dmabuf(struct gbm_device *gbm_device, GstMemory *me
return -1;
}

pthread_mutex_lock(&gbm_lock);

bo = gbm_bo_create(gbm_device, map_info.size, 1, GBM_FORMAT_R8, GBM_BO_USE_LINEAR);
if (bo == NULL) {
LOG_ERROR("Couldn't create GBM BO to copy video frame into.\n");
goto fail_unmap_buffer;
goto fail_unlock_gbm;
}

map_data = NULL;
Expand All @@ -440,13 +451,15 @@ UNUSED int dup_gst_memory_as_dmabuf(struct gbm_device *gbm_device, GstMemory *me

/// TODO: Should we dup the fd before we destroy the bo?
gbm_bo_destroy(bo);
pthread_mutex_unlock(&gbm_lock);
gst_memory_unmap(memory, &map_info);
return fd;

fail_destroy_bo:
gbm_bo_destroy(bo);

fail_unmap_buffer:
fail_unlock_gbm:
pthread_mutex_unlock(&gbm_lock);
gst_memory_unmap(memory, &map_info);
return -1;
}
Expand Down