Found in 2 comments on Hacker News
ctur · 2016-03-24 · Original thread
Two alternative, and better, choices, if you're willing to spend a few dollars (and hopefully expense it to your manager):

The Linux Programming Interface:

Advanced Programming in the UNIX Environment:

A not-too-distant third choice, Linux System Programming:

SwellJoe · 2015-04-22 · Original thread
There are several documentation projects about the Linux kernel, of wildly varying quality. Honestly, though, I believe you'd be better served by the Stevens books and the Tanenbaum MINIX book, if you're not already familiar with kernels or the UNIX architecture, in general. The Stevens books are, bar none, the best books about UNIX programming and TCP/IP network programming, and as far as I can tell every serious Linux developer has a working knowledge of Stevens, and many have referenced Stevens when discussing implementation details. And, of course, Linux was originally developed as kind of a response to MINIX and shares many characteristics, and was designed as a teaching operating system (there are other teaching operating systems, but none are probably closer to Linux than older MINIX versions).

Here's some Linux kernel specific stuff:

The first two have some age on them, but are still relatively reflective of the overall architecture of Linux, even if a lot of detail has changed. Anyway, these three are of reasonable quality. Some of the other stuff out there is pretty rough.

Fresh book recommendations delivered straight to your inbox every Thursday.