rcu: Documentation update
This commit applies a few updates based on a quick review of the RCU
documentations.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 31ef8fe..79e789b8 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -217,9 +217,14 @@
whether the increased speed is worth it.
8. Although synchronize_rcu() is slower than is call_rcu(), it
- usually results in simpler code. So, unless update performance
- is critically important or the updaters cannot block,
- synchronize_rcu() should be used in preference to call_rcu().
+ usually results in simpler code. So, unless update performance is
+ critically important, the updaters cannot block, or the latency of
+ synchronize_rcu() is visible from userspace, synchronize_rcu()
+ should be used in preference to call_rcu(). Furthermore,
+ kfree_rcu() usually results in even simpler code than does
+ synchronize_rcu() without synchronize_rcu()'s multi-millisecond
+ latency. So please take advantage of kfree_rcu()'s "fire and
+ forget" memory-freeing capabilities where it applies.
An especially important property of the synchronize_rcu()
primitive is that it automatically self-limits: if grace periods
@@ -268,7 +273,8 @@
e. Periodically invoke synchronize_rcu(), permitting a limited
number of updates per grace period.
- The same cautions apply to call_rcu_bh() and call_rcu_sched().
+ The same cautions apply to call_rcu_bh(), call_rcu_sched(),
+ call_srcu(), and kfree_rcu().
9. All RCU list-traversal primitives, which include
rcu_dereference(), list_for_each_entry_rcu(), and
@@ -296,9 +302,9 @@
all currently executing rcu_read_lock()-protected RCU read-side
critical sections complete. It does -not- necessarily guarantee
that all currently running interrupts, NMIs, preempt_disable()
- code, or idle loops will complete. Therefore, if you do not have
- rcu_read_lock()-protected read-side critical sections, do -not-
- use synchronize_rcu().
+ code, or idle loops will complete. Therefore, if your
+ read-side critical sections are protected by something other
+ than rcu_read_lock(), do -not- use synchronize_rcu().
Similarly, disabling preemption is not an acceptable substitute
for rcu_read_lock(). Code that attempts to use preemption
@@ -401,9 +407,9 @@
read-side critical sections. It is the responsibility of the
RCU update-side primitives to deal with this.
-17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and
- the __rcu sparse checks to validate your RCU code. These
- can help find problems as follows:
+17. Use CONFIG_PROVE_RCU, CONFIG_DEBUG_OBJECTS_RCU_HEAD, and the
+ __rcu sparse checks (enabled by CONFIG_SPARSE_RCU_POINTER) to
+ validate your RCU code. These can help find problems as follows:
CONFIG_PROVE_RCU: check that accesses to RCU-protected data
structures are carried out under the proper RCU