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-rw-r--r--Documentation/RCU/checklist.txt46
1 files changed, 39 insertions, 7 deletions
diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 790d1a812376..0c134f8afc6f 100644
--- a/Documentation/RCU/checklist.txt
+++ b/Documentation/RCU/checklist.txt
@@ -218,13 +218,22 @@ over a rather long period of time, but improvements are always welcome!
include:
a. Keeping a count of the number of data-structure elements
- used by the RCU-protected data structure, including those
- waiting for a grace period to elapse. Enforce a limit
- on this number, stalling updates as needed to allow
- previously deferred frees to complete.
-
- Alternatively, limit only the number awaiting deferred
- free rather than the total number of elements.
+ used by the RCU-protected data structure, including
+ those waiting for a grace period to elapse. Enforce a
+ limit on this number, stalling updates as needed to allow
+ previously deferred frees to complete. Alternatively,
+ limit only the number awaiting deferred free rather than
+ the total number of elements.
+
+ One way to stall the updates is to acquire the update-side
+ mutex. (Don't try this with a spinlock -- other CPUs
+ spinning on the lock could prevent the grace period
+ from ever ending.) Another way to stall the updates
+ is for the updates to use a wrapper function around
+ the memory allocator, so that this wrapper function
+ simulates OOM when there is too much memory awaiting an
+ RCU grace period. There are of course many other
+ variations on this theme.
b. Limiting update rate. For example, if updates occur only
once per hour, then no explicit rate limiting is required,
@@ -365,3 +374,26 @@ over a rather long period of time, but improvements are always welcome!
and the compiler to freely reorder code into and out of RCU
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:
+
+ CONFIG_PROVE_RCU: check that accesses to RCU-protected data
+ structures are carried out under the proper RCU
+ read-side critical section, while holding the right
+ combination of locks, or whatever other conditions
+ are appropriate.
+
+ CONFIG_DEBUG_OBJECTS_RCU_HEAD: check that you don't pass the
+ same object to call_rcu() (or friends) before an RCU
+ grace period has elapsed since the last time that you
+ passed that same object to call_rcu() (or friends).
+
+ __rcu sparse checks: tag the pointer to the RCU-protected data
+ structure with __rcu, and sparse will warn you if you
+ access that pointer without the services of one of the
+ variants of rcu_dereference().
+
+ These debugging aids can help you find problems that are
+ otherwise extremely difficult to spot.