[$] Toward a better list iterator for the kernel

Linked lists are conceptually straightforward; they tend to be taughttoward the beginning of entry-level data-structures classes. It might thusbe surprising that the kernel community is concerned about its longstandinglinked-list implementation and is not only looking for ways to solve someproblems, but has been struggling to find that solution. It now appearsthat some improvements might be at hand: after more than 30 years, the kerneldevelopers may have found a better way to safely iterate through a linked list.