[PATCH 7/9] srcu: Detect duplicate callback enqueue at registration

[Kunwu Chan]

Move the duplicate-callback check from srcu_do_enqueue() to
__call_srcu() entry so that detected duplicate registrations
are rejected before they reach the deferred-list enqueue path.
Report the callback address, function symbol, and object
information, rate-limited to the first three occurrences.

Signed-off-by: Kunwu Chan <chentao@xxxxxxxxxx>
---
 kernel/rcu/srcutree.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
index 1993ddbdb828..3838d9fdf532 100644
--- a/kernel/rcu/srcutree.c
+++ b/kernel/rcu/srcutree.c
@@ -27,6 +27,7 @@
 #include <linux/smp.h>
 #include <linux/delay.h>
 #include <linux/module.h>
+#include <linux/mm.h>
 #include <linux/slab.h>
 #include <linux/srcu.h>
 
@@ -1511,12 +1512,6 @@ static unsigned long srcu_gp_start_if_needed(struct srcu_struct *ssp,
 static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 			    rcu_callback_t func, bool do_norm)
 {
-	if (debug_rcu_head_queue(rhp)) {
-		/* Probable double call_srcu(), so leak the callback. */
-		WRITE_ONCE(rhp->func, srcu_leak_callback);
-		WARN_ONCE(1, "call_srcu(): Leaked duplicate callback\n");
-		return;
-	}
 	rhp->func = func;
 	(void)srcu_gp_start_if_needed(ssp, rhp, do_norm);
 }
@@ -1529,6 +1524,8 @@ static void srcu_do_enqueue(struct srcu_struct *ssp, struct rcu_head *rhp,
 static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 			rcu_callback_t func, bool do_norm)
 {
+	static atomic_t doublefrees;
+
 	/* Misaligned rcu_head! */
 	WARN_ON_ONCE((unsigned long)rhp & (sizeof(void *) - 1));
 
@@ -1539,6 +1536,16 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 	if (WARN_ON_ONCE(ssp->srcu_reader_flavor == SRCU_READ_FLAVOR_ATOMIC))
 		return; // Leak the callback rather than corrupt SRCU state.
 
+	if (debug_rcu_head_queue(rhp)) {
+		if (atomic_inc_return(&doublefrees) < 4) {
+			pr_err("%s(): Duplicate call_srcu() CB %p->%pS()\n",
+			       __func__, rhp, rhp->func);
+			mem_dump_obj(rhp);
+		}
+		WRITE_ONCE(rhp->func, srcu_leak_callback);
+		return;
+	}
+
 	/* Record the caller: the irq_work's stack says nothing about it. */
 	kasan_record_aux_stack(rhp);
 
@@ -1554,6 +1561,7 @@ static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
 		if (READ_ONCE(sndp->draining) && !in_nmi()) {
 			WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU),
 				  "call_srcu() re-entered during callback drain; leaking callback\n");
+			debug_rcu_head_unqueue(rhp);
 			return;
 		}
 		sdp = this_cpu_ptr(ssp->sda);
-- 
2.43.0