Visualize a piece of kernel (or driver) code wherein a large, global, doubly linked circular list (with a few thousand nodes) is being searched. Now, since the data structure is global (shared and writable), accessing it constitutes a critical section that requires protection.
Assuming a scenario where searching the list is a non-blocking operation, you'd typically use a spinlock to protect the critical section. A naive approach might propose not using a lock at all since we're only reading data within the list, not updating it. But, of course (as you have learned), even a read on shared writable data has to be protected to protect against an inadvertent write occurring simultaneously, thus resulting in a dirty or torn read.
So, we conclude that we require the spinlock; we imagine the pseudocode might look something like this:
spin_lock(mylist_lock);
for (p = &listhead; (p = next_node(p)) != &listhead; ) {
...
