[PATCH tip/core/rcu 20/86] rcu: Enable DEBUG_OBJECTS_RCU_HEAD from !PREEMPT

Paul E. McKenney
2011-05-01T13:35:51Z

From: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>

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>
---
kernel/rcupdate.c | 26 +++++++++++++++++++++-----
lib/Kconfig.debug | 2 +-
2 files changed, 22 insertions(+), 6 deletions(-)

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index f3240e9..b54d6d1 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);
diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index 93ce6de..3aa2780 100644
--- 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).

--
1.7.3.2