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-rw-r--r--kernel/rcupdate.c5
1 files changed, 5 insertions, 0 deletions
diff --git a/kernel/rcupdate.c b/kernel/rcupdate.c
index afd21d17c08..f3240e98792 100644
--- a/kernel/rcupdate.c
+++ b/kernel/rcupdate.c
@@ -214,6 +214,11 @@ 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.
*/
if (rcu_preempt_depth() != 0 || preempt_count() != 0 ||
irqs_disabled()) {