inter-group.cu: error: possible write-write race on ((char*)p)[0]:

inter-group.cu:4:3: write by thread (0, 0, 0) group (0, 0, 0)

  p[threadIdx.x] = threadIdx.x;

inter-group.cu:4:3: write by thread (0, 0, 0) group (1, 0, 0)

  p[threadIdx.x] = threadIdx.x;