wrs_shm_follow may not work for writer when writer reopens shmem
The problem may appear when a writer tries to reopen shmem for writing and reuse the existing data (e.g. after process restart/crash). If the shmem is mapped at the different address as it was before, then the offset calculated by wrs_shm_follow
for writer is wrong. It can never be assumed that the mapping address stays the same over restart of a process. The problem is since the introduction of shmem (2014).