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>

1 files changed, 21 insertions, 5 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f3240e987928..b54d6d18258c 100644
--- 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);