Merge branch 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip

* 'core-rcu-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/linux-2.6-tip:
  smp: Document transitivity for memory barriers.
  rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT.
  rcupdate: remove dead code
  rcu: add documentation saying which RCU flavor to choose
  rcutorture: Get rid of duplicate sched.h include
  rcu: call __rcu_read_unlock() in exit_rcu for tiny RCU

1 files changed, 5 insertions, 5 deletions

diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index a23a57a976d..f3240e98792 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -214,11 +214,12 @@ 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.
                  */
-#ifndef CONFIG_PREEMPT
-                WARN_ON(1);
-                return 0;
-#else
                 if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
                     irqs_disabled()) {
                         WARN_ON(1);
@@ -229,7 +230,6 @@ static int rcuhead_fixup_free(void *addr, enum debug_obj_state state)
                 rcu_barrier_bh();
                 debug_object_free(head, &rcuhead_debug_descr);
                 return 1;
-#endif
         default:
                 return 0;
         }