why does the kernel use mutex to protect the address_space structure

[Zheng Da]

Hello,

I try to understand why the kernel uses mutex to protect the
address_space structure. I checked the critical areas protected by
i_mmap_mutex, and didn't see these areas use IO. I don't see why we
can't use spin locks. Do I miss something? It seems most of critical
areas provided by i_mmap_mutex aren't very large.

Thanks,
Da