+ /*
+ * We need to take a reference to the real shm file to prevent the
+ * pointer from becoming stale in cases where the lifetime of the outer
+ * file extends beyond that of the shm segment. It's not usually
+ * possible, but it can happen during remap_file_pages() emulation as
+ * that unmaps the memory, then does ->mmap() via file reference only.
+ * We'll deny the ->mmap() if the shm segment was since removed, but to
+ * detect shm ID reuse we need to compare the file pointers.
+ */
+ sfd->file = get_file(shp->shm_file);