Merge branch 'master' into csb1725

[mv-sheeva.git] / Documentation / RCU / checklist.txt

diff --git a/Documentation/RCU/checklist.txt b/Documentation/RCU/checklist.txt
index 790d1a8123760211bdcb6427b75c1b4abf2b7210..0c134f8afc6f60b1316b9551577179f1b6dc3961 100644 (file)
--- 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.