rcu: kmemleak: Ignore kmemleak false positives when RCU-freeing objects

Since the actual slab freeing is deferred when calling kvfree_rcu(), so
is the kmemleak_free() callback informing kmemleak of the object
deletion. From the perspective of the kvfree_rcu() caller, the object is
freed and it may remove any references to it. Since kmemleak does not
scan the tree RCU internal data storing the pointer, it will report such
objects as leaks during the grace period.

Tell kmemleak to ignore such objects on the kvfree_call_rcu() path. Note
that the tiny RCU implementation does not have such issue since the
objects can be tracked from the rcu_ctrlblk structure.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Reported-by: Christoph Paasch <cpaasch@apple.com>

1 files changed, 9 insertions, 0 deletions

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cb1caefa8bd07..2ac39b5705df7 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -31,6 +31,7 @@
 #include <linux/bitops.h>
 #include <linux/export.h>
 #include <linux/completion.h>
+#include <linux/kmemleak.h>
 #include <linux/moduleparam.h>
 #include <linux/panic.h>
 #include <linux/panic_notifier.h>
@@ -3388,6 +3389,14 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 		success = true;
 	}
 
+	/*
+	 * The kvfree_rcu() caller considers the pointer freed at this point
+	 * and likely removes any references to it. Since the the actual slab
+	 * freeing (and kmemleak_free()) is deferred, tell kmemleak to ignore
+	 * this object (no scanning or false positives reporting).
+	 */
+	kmemleak_ignore(ptr);
+
 	// Set timer to drain after KFREE_DRAIN_JIFFIES.
 	if (rcu_scheduler_active == RCU_SCHEDULER_RUNNING)
 		schedule_delayed_monitor_work(krcp);