[PATCH v2 09/10] rcu-tasks: Detect duplicate callback enqueue

[Kunwu Chan]

Detect duplicate callback enqueue attempts in the generic
RCU Tasks callback registration path.  Use __ratelimit()
for the diagnostic output group.

Suggested-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>
---
 kernel/rcu/tasks.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h
index 5d7f234795b4..d5d060a5c4b6 100644
--- a/kernel/rcu/tasks.h
+++ b/kernel/rcu/tasks.h
@@ -6,6 +6,8 @@
  */
 
 #ifdef CONFIG_TASKS_RCU_GENERIC
+#include <linux/mm.h>
+#include <linux/ratelimit.h>
 #include "rcu_segcblist.h"
 
 ////////////////////////////////////////////////////////////////////////
@@ -339,6 +341,12 @@ static void call_rcu_tasks_iw_wakeup(struct irq_work *iwp)
 }
 
 // Enqueue a callback for the specified flavor of Tasks RCU.
+static void rcu_tasks_leak_callback(struct rcu_head *rhp) { }
+
+static DEFINE_RATELIMIT_STATE(rcu_tasks_dup_rs,
+			      DEFAULT_RATELIMIT_INTERVAL,
+			      DEFAULT_RATELIMIT_BURST);
+
 static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 				   struct rcu_tasks *rtp)
 {
@@ -358,6 +366,17 @@ static void call_rcu_tasks_generic(struct rcu_head *rhp, rcu_callback_t func,
 	if (WARN_ON_ONCE(!func))
 		return;
 
+	if (debug_rcu_head_queue(rhp)) {
+		if (__ratelimit(&rcu_tasks_dup_rs)) {
+			pr_err("%s(): Duplicate CB for %s, %p->%pS()\n",
+			       __func__, rtp->name, rhp, rhp->func);
+			mem_dump_obj(rhp);
+			dump_stack();
+		}
+		WRITE_ONCE(rhp->func, rcu_tasks_leak_callback);
+		return;
+	}
+
 	rhp->next = NULL;
 	rhp->func = func;
 	local_irq_save(flags);
@@ -586,6 +605,7 @@ static void rcu_tasks_invoke_cbs(struct rcu_tasks *rtp, struct rcu_tasks_percpu
 	raw_spin_unlock_irqrestore_rcu_node(rtpcp, flags);
 	len = rcl.len;
 	for (rhp = rcu_cblist_dequeue(&rcl); rhp; rhp = rcu_cblist_dequeue(&rcl)) {
+		debug_rcu_head_unqueue(rhp);
 		debug_rcu_head_callback(rhp);
 		local_bh_disable();
 		rhp->func(rhp);
-- 
2.43.0