selftests/bpf: Add tests for rbtree API interaction in sleepable progs

Confirm that the following sleepable prog states fail verification:
  * bpf_rcu_read_unlock before bpf_spin_unlock
     * RCU CS will last at least as long as spin_lock CS

Also confirm that correct usage passes verification, specifically:
  * Explicit use of bpf_rcu_read_{lock, unlock} in sleepable test prog
  * Implied RCU CS due to spin_lock CS

None of the selftest progs actually attach to bpf_testmod's
bpf_testmod_test_read.

Signed-off-by: Dave Marchevsky <davemarchevsky@fb.com>
Link: https://lore.kernel.org/r/20230821193311.3290257-8-davemarchevsky@fb.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

Author: davemarchevsky

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

@@ -8,6 +8,9 @@
 #include "bpf_misc.h"
 #include "bpf_experimental.h"
 
+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
+
 struct node_data {
 	long key;
 	long list_data;
@@ -497,4 +500,72 @@ long rbtree_wrong_owner_remove_fail_a2(void *ctx)
 	return 0;
 }
 
+SEC("?fentry.s/bpf_testmod_test_read")
+__success
+int BPF_PROG(rbtree_sleepable_rcu,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	struct bpf_rb_node *rb;
+	struct node_data *n, *m = NULL;
+
+	n = bpf_obj_new(typeof(*n));
+	if (!n)
+		return 0;
+
+	bpf_rcu_read_lock();
+	bpf_spin_lock(&lock);
+	bpf_rbtree_add(&root, &n->r, less);
+	rb = bpf_rbtree_first(&root);
+	if (!rb)
+		goto err_out;
+
+	rb = bpf_rbtree_remove(&root, rb);
+	if (!rb)
+		goto err_out;
+
+	m = container_of(rb, struct node_data, r);
+
+err_out:
+	bpf_spin_unlock(&lock);
+	bpf_rcu_read_unlock();
+	if (m)
+		bpf_obj_drop(m);
+	return 0;
+}
+
+SEC("?fentry.s/bpf_testmod_test_read")
+__success
+int BPF_PROG(rbtree_sleepable_rcu_no_explicit_rcu_lock,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	struct bpf_rb_node *rb;
+	struct node_data *n, *m = NULL;
+
+	n = bpf_obj_new(typeof(*n));
+	if (!n)
+		return 0;
+
+	/* No explicit bpf_rcu_read_lock */
+	bpf_spin_lock(&lock);
+	bpf_rbtree_add(&root, &n->r, less);
+	rb = bpf_rbtree_first(&root);
+	if (!rb)
+		goto err_out;
+
+	rb = bpf_rbtree_remove(&root, rb);
+	if (!rb)
+		goto err_out;
+
+	m = container_of(rb, struct node_data, r);
+
+err_out:
+	bpf_spin_unlock(&lock);
+	/* No explicit bpf_rcu_read_unlock */
+	if (m)
+		bpf_obj_drop(m);
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";

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

@@ -13,6 +13,9 @@ struct node_acquire {
 	struct bpf_refcount refcount;
 };
 
+extern void bpf_rcu_read_lock(void) __ksym;
+extern void bpf_rcu_read_unlock(void) __ksym;
+
 #define private(name) SEC(".data." #name) __hidden __attribute__((aligned(8)))
 private(A) struct bpf_spin_lock glock;
 private(A) struct bpf_rb_root groot __contains(node_acquire, node);
@@ -71,4 +74,29 @@ long rbtree_refcounted_node_ref_escapes_owning_input(void *ctx)
 	return 0;
 }
 
+SEC("?fentry.s/bpf_testmod_test_read")
+__failure __msg("function calls are not allowed while holding a lock")
+int BPF_PROG(rbtree_fail_sleepable_lock_across_rcu,
+	     struct file *file, struct kobject *kobj,
+	     struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len)
+{
+	struct node_acquire *n;
+
+	n = bpf_obj_new(typeof(*n));
+	if (!n)
+		return 0;
+
+	/* spin_{lock,unlock} are in different RCU CS */
+	bpf_rcu_read_lock();
+	bpf_spin_lock(&glock);
+	bpf_rbtree_add(&groot, &n->node, less);
+	bpf_rcu_read_unlock();
+
+	bpf_rcu_read_lock();
+	bpf_spin_unlock(&glock);
+	bpf_rcu_read_unlock();
+
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";