diff --git a/Documentation/RCU/Design/Data-Structures/Data-Structures.html b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
index 28b241074c86..3ed5f0182bc4 100644
--- a/Documentation/RCU/Design/Data-Structures/Data-Structures.html
+++ b/Documentation/RCU/Design/Data-Structures/Data-Structures.html
@@ -928,17 +928,24 @@ this rcu_segcblist structure, not the ->head
pointer.
The reason for this is that all the ready-to-invoke callbacks
(that is, those in the RCU_DONE_TAIL segment) are extracted
-all at once at callback-invocation time.
+all at once at callback-invocation time (rcu_do_batch), due
+to which ->head may be set to NULL if there are no not-done
+callbacks remaining in the rcu_segcblist.
If callback invocation must be postponed, for example, because a
high-priority process just woke up on this CPU, then the remaining
-callbacks are placed back on the RCU_DONE_TAIL segment.
-Either way, the ->len and ->len_lazy counts
-are adjusted after the corresponding callbacks have been invoked, and so
-again it is the ->len count that accurately reflects whether
-or not there are callbacks associated with this rcu_segcblist
-structure.
+callbacks are placed back on the RCU_DONE_TAIL segment and
+->head once again points to the start of the segment.
+In short, the head field can briefly be NULL even though the
+CPU has callbacks present the entire time.
+Therefore, it is not appropriate to test the ->head pointer
+for NULL.
+
+In contrast, the ->len and ->len_lazy counts
+are adjusted only after the corresponding callbacks have been invoked.
+This means that the ->len count is zero only if
+the rcu_segcblist structure really is devoid of callbacks.
Of course, off-CPU sampling of the ->len count requires
-the use of appropriate synchronization, for example, memory barriers.
+careful use of appropriate synchronization, for example, memory barriers.
This synchronization can be a bit subtle, particularly in the case
of rcu_barrier().