Lec10 Multiprocessors and locking (Frans) 准备工作，阅读【1】中第6章，和【2】 【1】https://pdos.csail.mit.edu/6.828/2020/xv6/book-riscv-rev1.pdf 【2】https://github.com/mit-pdos/xv6-riscv/blob/riscv/kernel/spinlock.h 【3】https://github.com/mit-pdos/xv6-riscv/blob/riscv/kernel/spinlock.c