The final read by client B (in a shaded bar) is not linearizable. The operation is concurrent with C’s cas write, which updates x from 2 to 4. In the absence of other requests, it would be okay for B’s read to return 2. However, client A has already read the new value 4 before B’s read started, so B is not allowed to read an older value than A. Again, it’s the same situation as with Alice and Bob in Figure 9-1
