System information (version)

• OpenCV => 4.4.0
• Operating System / Platform => Windows 10 64 Bit
• Compiler => Visual Studio 2019 (16.6.2)

Detailed description

When compiled in debug mode I get the following warning logged to the console from when executing the cv::dnn::forward function when using the opencl target.

! OPENCV warning: getUMat()/getMat() call chain possible problem.
!                 Base object is dead, while nested/derived object is still alive or processed.
!                 Please check lifetime of UMat/Mat objects!

The program seems to be running fine even with the warning indicating that it is the warning that is invalid.
This warning is not produced with a release compilation or when running without setting a prefrable target.

Steps to reproduce

I can reproduce the issue with a modified version of the learnopencv dnn example at https://github.com/spmallick/learnopencv/blob/master/FaceDetectionComparison/face_detection_opencv_dnn.cpp

The following additional line is added after line 64 to trigger the warning to be created.

  net.setPreferableTarget(cv::dnn::DNN_TARGET_OPENCL);

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc