For the Linux kernel, there is an excellent book called "Linux Core Kernel Commentary" (which is based off the SVR4 Lion's Commentary book), which has the sourc

For the Linux kernel, there is an excellent book called "Linux Core Kernel Commentary" (which is based off the SVR4 Lion's Commentary book), which has the source of the kernel (an old version) printed out and then a commentary on all the bits (code and data structures). It was an eye opener for me. As for OS theory, "Operating Systems Vade Macum" and "Operating Systems Design and Implementation" are my favorites.