1 files changed, 13 insertions, 5 deletions

diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 6ef692667e2f..8e8cdc2430b9 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -834,6 +834,8 @@ SRCU:	Critical sections	Grace period		Barrier
 
         srcu_read_lock          synchronize_srcu        N/A
         srcu_read_unlock        synchronize_srcu_expedited
+        srcu_read_lock_raw
+        srcu_read_unlock_raw
         srcu_dereference
 
 SRCU:   Initialization/cleanup
@@ -855,27 +857,33 @@ list can be helpful:
 
 a.      Will readers need to block?  If so, you need SRCU.
 
-b.      What about the -rt patchset?  If readers would need to block
+b.      Is it necessary to start a read-side critical section in a
+        hardirq handler or exception handler, and then to complete
+        this read-side critical section in the task that was
+        interrupted?  If so, you need SRCU's srcu_read_lock_raw() and
+        srcu_read_unlock_raw() primitives.
+
+c.      What about the -rt patchset?  If readers would need to block
         in an non-rt kernel, you need SRCU.  If readers would block
         in a -rt kernel, but not in a non-rt kernel, SRCU is not
         necessary.
 
-c.      Do you need to treat NMI handlers, hardirq handlers,
+d.      Do you need to treat NMI handlers, hardirq handlers,
         and code segments with preemption disabled (whether
         via preempt_disable(), local_irq_save(), local_bh_disable(),
         or some other mechanism) as if they were explicit RCU readers?
         If so, you need RCU-sched.
 
-d.      Do you need RCU grace periods to complete even in the face
+e.      Do you need RCU grace periods to complete even in the face
         of softirq monopolization of one or more of the CPUs?  For
         example, is your code subject to network-based denial-of-service
         attacks?  If so, you need RCU-bh.
 
-e.      Is your workload too update-intensive for normal use of
+f.      Is your workload too update-intensive for normal use of
         RCU, but inappropriate for other synchronization mechanisms?
         If so, consider SLAB_DESTROY_BY_RCU.  But please be careful!
 
-f.      Otherwise, use RCU.
+g.      Otherwise, use RCU.
 
 Of course, this all assumes that you have determined that RCU is in fact
 the right tool for your job.