why use barrier() in binder_mmap function?

[Zhao Junmin]

Hi All:

   Now I am reading binder code, 

buffer = proc->buffer;

INIT_LIST_HEAD(&proc->buffers);

list_add(&buffer->entry, &proc->buffers);

buffer->free = 1;

binder_insert_free_buffer(proc, buffer);

proc->free_async_space = proc->buffer_size / 2;

barrier();

proc->files = get_files_struct(current);

proc->vma = vma;

proc->vma_vm_mm = vma->vm_mm;

why use barrier in here?

According the kernel/Documentation/memory-barriers.txt

barrier is an explicit compiler barrier function that prevents the

compiler from moving the memory accesses either side of it to the other side:

if no barrier here, which code will have issue in here?

Thanks

Zhaojunmin