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

commit 5f98fd034ca6fd1ab8c91a3488968a0e9caaabf6 upstream.

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 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>
Closes: https://lore.kernel.org/all/F903A825-F05F-4B77-A2B5-7356282FBA2C@apple.com/
Cc: <stable@vger.kernel.org>
Tested-by: Christoph Paasch <cpaasch@apple.com>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 835c45416b2385ee6b67065fe06f66edce9e39d3..66c1ca01dd0e988acc5724aa2176ebbc15e3e028 100644 (file)
--- 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>
@@ -3609,6 +3610,14 @@ void kvfree_call_rcu(struct rcu_head *head, rcu_callback_t func)
 
        WRITE_ONCE(krcp->count, krcp->count + 1);
 
+       /*
+        * The kvfree_rcu() caller considers the pointer freed at this point
+        * and likely removes any references to it. Since 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 &&
            !krcp->monitor_todo) {