selftests: bpf: Add tests for unbalanced rcu_read_lock

As verifier now supports nested rcu critical sections, add new test
cases to make sure unbalanced usage of rcu_read_lock()/unlock() is
rejected.

Signed-off-by: Puranjay Mohan <[email protected]>

Author: puranjaymohan

tools/testing/selftests/bpf/prog_tests/rcu_read_lock.c

@@ -79,6 +79,8 @@ static const char * const inproper_region_tests[] = {
 	"non_sleepable_rcu_mismatch",
 	"inproper_sleepable_helper",
 	"inproper_sleepable_kfunc",
+	"nested_rcu_region_unbalanced_1",
+	"nested_rcu_region_unbalanced_2",
 	"rcu_read_lock_global_subprog_lock",
 	"rcu_read_lock_global_subprog_unlock",
 	"rcu_read_lock_sleepable_helper_global_subprog",

tools/testing/selftests/bpf/progs/rcu_read_lock.c

@@ -278,6 +278,46 @@ int nested_rcu_region(void *ctx)
 	return 0;
 }
 
+SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
+int nested_rcu_region_unbalanced_1(void *ctx)
+{
+	struct task_struct *task, *real_parent;
+
+	/* nested rcu read lock regions */
+	task = bpf_get_current_task_btf();
+	bpf_rcu_read_lock();
+	bpf_rcu_read_lock();
+	real_parent = task->real_parent;
+	if (!real_parent)
+		goto out;
+	(void)bpf_task_storage_get(&map_a, real_parent, 0, 0);
+out:
+	bpf_rcu_read_unlock();
+	bpf_rcu_read_unlock();
+	bpf_rcu_read_unlock();
+	return 0;
+}
+
+SEC("?fentry.s/" SYS_PREFIX "sys_nanosleep")
+int nested_rcu_region_unbalanced_2(void *ctx)
+{
+	struct task_struct *task, *real_parent;
+
+	/* nested rcu read lock regions */
+	task = bpf_get_current_task_btf();
+	bpf_rcu_read_lock();
+	bpf_rcu_read_lock();
+	bpf_rcu_read_lock();
+	real_parent = task->real_parent;
+	if (!real_parent)
+		goto out;
+	(void)bpf_task_storage_get(&map_a, real_parent, 0, 0);
+out:
+	bpf_rcu_read_unlock();
+	bpf_rcu_read_unlock();
+	return 0;
+}
+
 SEC("?fentry.s/" SYS_PREFIX "sys_getpgid")
 int task_trusted_non_rcuptr(void *ctx)
 {