rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPT

The prohibition of DEBUG_OBJECTS_RCU_HEAD from !PREEMPT was due to the
fixup actions.  So just produce a warning from !PREEMPT.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f3240e9..b54d6d1 100644 (file)
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -142,7 +142,14 @@ static int rcuhead_fixup_init(void *addr, enum debug_obj_state state)
                 * Ensure that queued callbacks are all executed.
                 * If we detect that we are nested in a RCU read-side critical
                 * section, we should simply fail, otherwise we would deadlock.
+                * In !PREEMPT configurations, there is no way to tell if we are
+                * in a RCU read-side critical section or not, so we never
+                * attempt any fixup and just print a warning.
                 */
+#ifndef CONFIG_PREEMPT
+               WARN_ON(1);
+               return 0;
+#endif
                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                    irqs_disabled()) {
                        WARN_ON(1);
@@ -184,7 +191,14 @@ static int rcuhead_fixup_activate(void *addr, enum debug_obj_state state)
                 * Ensure that queued callbacks are all executed.
                 * If we detect that we are nested in a RCU read-side critical
                 * section, we should simply fail, otherwise we would deadlock.
+                * In !PREEMPT configurations, there is no way to tell if we are
+                * in a RCU read-side critical section or not, so we never
+                * attempt any fixup and just print a warning.
                 */
+#ifndef CONFIG_PREEMPT
+               WARN_ON(1);
+               return 0;
+#endif
                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                    irqs_disabled()) {
                        WARN_ON(1);
@@ -214,12 +228,14 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
                 * Ensure that queued callbacks are all executed.
                 * If we detect that we are nested in a RCU read-side critical
                 * section, we should simply fail, otherwise we would deadlock.
-                * Note that the machinery to reliably determine whether
-                * or not we are in an RCU read-side critical section
-                * exists only in the preemptible RCU implementations
-                * (TINY_PREEMPT_RCU and TREE_PREEMPT_RCU), which is why
-                * DEBUG_OBJECTS_RCU_HEAD is disallowed if !PREEMPT.
+                * In !PREEMPT configurations, there is no way to tell if we are
+                * in a RCU read-side critical section or not, so we never
+                * attempt any fixup and just print a warning.
                 */
+#ifndef CONFIG_PREEMPT
+               WARN_ON(1);
+               return 0;
+#endif
                if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                    irqs_disabled()) {
                        WARN_ON(1);

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93ce6de..3aa2780 100644 (file)
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -337,7 +337,7 @@ config DEBUG_OBJECTS_WORK
 
 config DEBUG_OBJECTS_RCU_HEAD
        bool "Debug RCU callbacks objects"
-       depends on DEBUG_OBJECTS && PREEMPT
+       depends on DEBUG_OBJECTS
        help
          Enable this to turn on debugging of RCU list heads (call_rcu() usage).