[PATCH] rcu: Make tiny RCU support leak callbacks for debug-object errors

[Zqiang]

Currently, only tree RCU support leak callbacks setting when do
duplicate call_rcu(). this commit add leak callbacks setting when
fo duplicate call_rcu() for tiny RCU.

Signed-off-by: Zqiang <qiang1.zhang@xxxxxxxxx>
---
 kernel/rcu/tiny.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index f0561ee16b9c..b3c64cee0313 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -158,6 +158,10 @@ void synchronize_rcu(void)
 }
 EXPORT_SYMBOL_GPL(synchronize_rcu);
 
+static void tiny_rcu_leak_callback(struct rcu_head *rhp)
+{
+}
+
 /*
  * Post an RCU callback to be invoked after the end of an RCU grace
  * period.  But since we have but one CPU, that would be after any
@@ -165,9 +169,18 @@ EXPORT_SYMBOL_GPL(synchronize_rcu);
  */
 void call_rcu(struct rcu_head *head, rcu_callback_t func)
 {
+	static atomic_t doublefrees;
 	unsigned long flags;
 
-	debug_rcu_head_queue(head);
+	if (debug_rcu_head_queue(head)) {
+		if (atomic_inc_return(&doublefrees) < 4) {
+			pr_err("%s(): Double-freed CB %p->%pS()!!!  ", __func__, head, head->func);
+			mem_dump_obj(head);
+		}
+		WRITE_ONCE(head->func, tiny_rcu_leak_callback);
+		return;
+	}
+
 	head->func = func;
 	head->next = NULL;
 
-- 
2.25.1