cudaMemcpy Segmentation Fault
When calling cudaMemcpy to transfer data from device to host, users may encounter a segmentation fault. This often stems from improper handling of device pointers.
The Issue
The following code demonstrates the issue:
cudaMemcpy(CurrentGrid->cdata[i], Grid_dev->cdata[i], size*sizeof(float),\ cudaMemcpyDeviceToHost);
Here, Grid_dev is a device pointer to a grid class object. Attempting to directly dereference this pointer in the cudaMemcpy call may lead to a segmentation fault.
Solution
To resolve this issue, an intermediate pointer must be created on the host to reference the device pointer. The following code outlines the revised solution:
float * A; cudaMalloc((void**)&A, sizeof(float)); ... ... cudaMemcpy(&A, &(Grid_dev->cdata[i]), sizeof(float *), cudaMemcpyDeviceToHost); CurrentGrid->cdata[i] = new float[size]; cudaMemcpy(CurrentGrid->cdata[i], A, size*sizeof(float), cudaMemcpyDeviceToHost);
In this modified code, A is a host pointer that initially points to a device pointer. By copying the value of Grid_dev->cdata[i] to A using cudaMemcpy, we effectively transfer the device pointer to the host. Subsequently, CurrentGrid->cdata[i] can be assigned to a new float array on the host, and the data can be copied from the device pointer A to this array.
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