rcu: define __rcu address space modifier for sparse
This commit provides definitions for the __rcu annotation defined earlier.
This annotation permits sparse to check for correct use of RCU-protected
pointers. If a pointer that is annotated with __rcu is accessed
directly (as opposed to via rcu_dereference(), rcu_assign_pointer(),
or one of their variants), sparse can be made to complain. To enable
such complaints, use the new default-disabled CONFIG_SPARSE_RCU_POINTER
kernel configuration option. Please note that these sparse complaints are
intended to be a debugging aid, -not- a code-style-enforcement mechanism.
There are special rcu_dereference_protected() and rcu_access_pointer()
accessors for use when RCU read-side protection is not required, for
example, when no other CPU has access to the data structure in question
or while the current CPU hold the update-side lock.
This patch also updates a number of docbook comments that were showing
their age.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Christopher Li <sparse@chrisli.org>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 1b4afd2..12465f2 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -539,6 +539,19 @@
disabling, allowing multiple RCU-lockdep warnings to be printed
on a single reboot.
+config SPARSE_RCU_POINTER
+ bool "RCU debugging: sparse-based checks for pointer usage"
+ default n
+ help
+ This feature enables the __rcu sparse annotation for
+ RCU-protected pointers. This annotation will cause sparse
+ to flag any non-RCU used of annotated pointers. This can be
+ helpful when debugging RCU usage. Please note that this feature
+ is not intended to enforce code cleanliness; it is instead merely
+ a debugging aid.
+
+ Say Y to make sparse flag questionable use of RCU-protected pointers
+
Say N if you are unsure.
config LOCKDEP