Merge branch 'rcu/next' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-2.6-rcu into core/rcu

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.