[PATCH 1/1] rcu/kvfree: Add runtime sleep check for single argument

["Uladzislau Rezki (Sony)" <urezki@gmail.com>]

A single argument can be invoked only from a sleepable
context. There is already a might_sleep() check to mitigate
such cases. The problem is that it requires a kernel to
be built with a CONFIG_DEBUG_ATOMIC_SLEEP option.

In order to improve an extra runtime_assert_can_sleep()
function is introduced by this patch. It is a run-time
checking. Please note it only covers PREEMPT kernels.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
---
 kernel/rcu/tree.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d155f2594317..bb798f07e768 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3232,6 +3232,19 @@ add_ptr_to_bulk_krc_lock(struct kfree_rcu_cpu **krcp,
 	return true;
 }
 
+static void
+runtime_assert_can_sleep(void)
+{
+	if (!IS_ENABLED(CONFIG_PREEMPT_COUNT))
+		return;
+
+	if (preemptible())
+		return;
+
+	WARN_ONCE(1, "in_atomic(): %d, irqs_disabled(): %d, pid: %d, name: %s\n",
+		in_atomic(), irqs_disabled(), current->pid, current->comm);
+}
+
 /*
  * Queue a request for lazy invocation of the appropriate free routine
  * after a grace period.  Please note that three paths are maintained,
@@ -3257,8 +3270,10 @@ void kvfree_call_rcu(struct rcu_head *head, void *ptr)
 	 * only. For other places please embed an rcu_head to
 	 * your data.
 	 */
-	if (!head)
+	if (!head) {
+		runtime_assert_can_sleep();
 		might_sleep();
+	}
 
 	// Queue the object but don't yet schedule the batch.
 	if (debug_rcu_head_queue(ptr)) {
-- 
2.30.2