rcu: Add documentation for raw SRCU read-side primitives

Update various files in Documentation/RCU to reflect srcu_read_lock_raw()
and srcu_read_unlock_raw().  Credit to Peter Zijlstra for suggesting
use of the existing _raw suffix instead of the earlier bulkref names.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

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.