how to define local structure in opencl

I have the following struct in the kernel

err = clEnqueueReadBuffer(queue, fragments_buf_mem, CL_TRUE, 0, width * height*sizeof(Fragment), &fragments[0], 0, NULL, &kernel_event);

fragments_buf_mem = clCreateBuffer(context, CL_MEM_READ_WRITE, width * height*sizeof(Fragment), NULL, &err);


struct Fragment {
    float pos[3];
    float nor[3];
    float col[3];
    bool isCovered;
};

I'm trying to assing a global fragments buffer locally to a struct

Kernel definition

__kernel void fragment_shader(__global struct Fragment* fragments, __global struct Triangle_* triangles, int triCount)

Inside the kernel I'm trying to define a local structure and assign variables to it struct Fragment f;

        f.pos[0] = (float)w0 * v0Raster.y;
        /*              
        f.pos[1] = (float)w1 * v1Raster.y;
        f.pos[2] = (float)w2 * v2Raster.z;

        f.nor[0] = (float)w0 * v1Raster_n.x;
        f.nor[1] = (float)w1 * v1Raster_n.y;
        f.nor[2] = (float)w2 * v2Raster_n.z;

        f.col[0] = (float)w0 * v1Raster_c.x;
        f.col[1] = (float)w1 * v1Raster_c.y;
        f.col[2] = (float)w2 * v2Raster_c.z;
        */

        fragments[x + y * imageWidth] = f;

I can't enqueue the kernel and I get an exception. However when I remove the commented code, and just use f <-- struct alone, I can enqueue the kernel, only we setting data to the local structure fragment, I get a crash.