selftests/bpf: Add a test for btf_type_tag "percpu"

Add test for percpu btf_type_tag. Similar to the "user" tag, we test
the following cases:

 1. __percpu struct field.
 2. __percpu as function parameter.
 3. per_cpu_ptr() accepts dynamically allocated __percpu memory.

Because the test for "user" and the test for "percpu" are very similar,
a little bit of refactoring has been done in btf_tag.c. Basically, both
tests share the same function for loading vmlinux and module btf.

Example output from log:

 > ./test_progs -v -t btf_tag

 libbpf: prog 'test_percpu1': BPF program load failed: Permission denied
 libbpf: prog 'test_percpu1': -- BEGIN PROG LOAD LOG --
 ...
 ; g = arg->a;
 1: (61) r1 = *(u32 *)(r1 +0)
 R1 is ptr_bpf_testmod_btf_type_tag_1 access percpu memory: off=0
 ...
 test_btf_type_tag_mod_percpu:PASS:btf_type_tag_percpu 0 nsec
 #26/6 btf_tag/btf_type_tag_percpu_mod1:OK

 libbpf: prog 'test_percpu2': BPF program load failed: Permission denied
 libbpf: prog 'test_percpu2': -- BEGIN PROG LOAD LOG --
 ...
 ; g = arg->p->a;
 2: (61) r1 = *(u32 *)(r1 +0)
 R1 is ptr_bpf_testmod_btf_type_tag_1 access percpu memory: off=0
 ...
 test_btf_type_tag_mod_percpu:PASS:btf_type_tag_percpu 0 nsec
 #26/7 btf_tag/btf_type_tag_percpu_mod2:OK

 libbpf: prog 'test_percpu_load': BPF program load failed: Permission denied
 libbpf: prog 'test_percpu_load': -- BEGIN PROG LOAD LOG --
 ...
 ; g = (__u64)cgrp->rstat_cpu->updated_children;
 2: (79) r1 = *(u64 *)(r1 +48)
 R1 is ptr_cgroup_rstat_cpu access percpu memory: off=48
 ...
 test_btf_type_tag_vmlinux_percpu:PASS:btf_type_tag_percpu_load 0 nsec
 #26/8 btf_tag/btf_type_tag_percpu_vmlinux_load:OK

 load_btfs:PASS:could not load vmlinux BTF 0 nsec
 test_btf_type_tag_vmlinux_percpu:PASS:btf_type_tag_percpu 0 nsec
 test_btf_type_tag_vmlinux_percpu:PASS:btf_type_tag_percpu_helper 0 nsec
 #26/9 btf_tag/btf_type_tag_percpu_vmlinux_helper:OK

Signed-off-by: Hao Luo <haoluo@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20220304191657.981240-5-haoluo@google.com

tools/testing/selftests/bpf/bpf_testmod/bpf_testmod.c

@@ -33,6 +33,10 @@ struct bpf_testmod_btf_type_tag_2 {
 	struct bpf_testmod_btf_type_tag_1 __user *p;
 };
 
+struct bpf_testmod_btf_type_tag_3 {
+	struct bpf_testmod_btf_type_tag_1 __percpu *p;
+};
+
 noinline int
 bpf_testmod_test_btf_type_tag_user_1(struct bpf_testmod_btf_type_tag_1 __user *arg) {
 	BTF_TYPE_EMIT(func_proto_typedef);
@@ -46,6 +50,16 @@ bpf_testmod_test_btf_type_tag_user_2(struct bpf_testmod_btf_type_tag_2 *arg) {
 	return arg->p->a;
 }
 
+noinline int
+bpf_testmod_test_btf_type_tag_percpu_1(struct bpf_testmod_btf_type_tag_1 __percpu *arg) {
+	return arg->a;
+}
+
+noinline int
+bpf_testmod_test_btf_type_tag_percpu_2(struct bpf_testmod_btf_type_tag_3 *arg) {
+	return arg->p->a;
+}
+
 noinline int bpf_testmod_loop_test(int n)
 {
 	int i, sum = 0;

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

@@ -10,6 +10,7 @@ struct btf_type_tag_test {
 };
 #include "btf_type_tag.skel.h"
 #include "btf_type_tag_user.skel.h"
+#include "btf_type_tag_percpu.skel.h"
 
 static void test_btf_decl_tag(void)
 {
@@ -43,38 +44,81 @@ static void test_btf_type_tag(void)
 	btf_type_tag__destroy(skel);
 }
 
-static void test_btf_type_tag_mod_user(bool load_test_user1)
+/* loads vmlinux_btf as well as module_btf. If the caller passes NULL as
+ * module_btf, it will not load module btf.
+ *
+ * Returns 0 on success.
+ * Return -1 On error. In case of error, the loaded btf will be freed and the
+ * input parameters will be set to pointing to NULL.
+ */
+static int load_btfs(struct btf **vmlinux_btf, struct btf **module_btf,
+		     bool needs_vmlinux_tag)
 {
 	const char *module_name = "bpf_testmod";
-	struct btf *vmlinux_btf, *module_btf;
-	struct btf_type_tag_user *skel;
 	__s32 type_id;
-	int err;
 
 	if (!env.has_testmod) {
 		test__skip();
-		return;
+		return -1;
 	}
 
-	/* skip the test if the module does not have __user tags */
-	vmlinux_btf = btf__load_vmlinux_btf();
-	if (!ASSERT_OK_PTR(vmlinux_btf, "could not load vmlinux BTF"))
-		return;
+	*vmlinux_btf = btf__load_vmlinux_btf();
+	if (!ASSERT_OK_PTR(*vmlinux_btf, "could not load vmlinux BTF"))
+		return -1;
 
-	module_btf = btf__load_module_btf(module_name, vmlinux_btf);
-	if (!ASSERT_OK_PTR(module_btf, "could not load module BTF"))
+	if (!needs_vmlinux_tag)
+		goto load_module_btf;
+
+	/* skip the test if the vmlinux does not have __user tags */
+	type_id = btf__find_by_name_kind(*vmlinux_btf, "user", BTF_KIND_TYPE_TAG);
+	if (type_id <= 0) {
+		printf("%s:SKIP: btf_type_tag attribute not in vmlinux btf", __func__);
+		test__skip();
+		goto free_vmlinux_btf;
+	}
+
+load_module_btf:
+	/* skip loading module_btf, if not requested by caller */
+	if (!module_btf)
+		return 0;
+
+	*module_btf = btf__load_module_btf(module_name, *vmlinux_btf);
+	if (!ASSERT_OK_PTR(*module_btf, "could not load module BTF"))
 		goto free_vmlinux_btf;
 
-	type_id = btf__find_by_name_kind(module_btf, "user", BTF_KIND_TYPE_TAG);
+	/* skip the test if the module does not have __user tags */
+	type_id = btf__find_by_name_kind(*module_btf, "user", BTF_KIND_TYPE_TAG);
 	if (type_id <= 0) {
 		printf("%s:SKIP: btf_type_tag attribute not in %s", __func__, module_name);
 		test__skip();
 		goto free_module_btf;
 	}
 
+	return 0;
+
+free_module_btf:
+	btf__free(*module_btf);
+free_vmlinux_btf:
+	btf__free(*vmlinux_btf);
+
+	*vmlinux_btf = NULL;
+	if (module_btf)
+		*module_btf = NULL;
+	return -1;
+}
+
+static void test_btf_type_tag_mod_user(bool load_test_user1)
+{
+	struct btf *vmlinux_btf = NULL, *module_btf = NULL;
+	struct btf_type_tag_user *skel;
+	int err;
+
+	if (load_btfs(&vmlinux_btf, &module_btf, /*needs_vmlinux_tag=*/false))
+		return;
+
 	skel = btf_type_tag_user__open();
 	if (!ASSERT_OK_PTR(skel, "btf_type_tag_user"))
-		goto free_module_btf;
+		goto cleanup;
 
 	bpf_program__set_autoload(skel->progs.test_sys_getsockname, false);
 	if (load_test_user1)
@@ -87,34 +131,23 @@ static void test_btf_type_tag_mod_user(bool load_test_user1)
 
 	btf_type_tag_user__destroy(skel);
 
-free_module_btf:
+cleanup:
 	btf__free(module_btf);
-free_vmlinux_btf:
 	btf__free(vmlinux_btf);
 }
 
 static void test_btf_type_tag_vmlinux_user(void)
 {
 	struct btf_type_tag_user *skel;
-	struct btf *vmlinux_btf;
-	__s32 type_id;
+	struct btf *vmlinux_btf = NULL;
 	int err;
 
-	/* skip the test if the vmlinux does not have __user tags */
-	vmlinux_btf = btf__load_vmlinux_btf();
-	if (!ASSERT_OK_PTR(vmlinux_btf, "could not load vmlinux BTF"))
+	if (load_btfs(&vmlinux_btf, NULL, /*needs_vmlinux_tag=*/true))
 		return;
 
-	type_id = btf__find_by_name_kind(vmlinux_btf, "user", BTF_KIND_TYPE_TAG);
-	if (type_id <= 0) {
-		printf("%s:SKIP: btf_type_tag attribute not in vmlinux btf", __func__);
-		test__skip();
-		goto free_vmlinux_btf;
-	}
-
 	skel = btf_type_tag_user__open();
 	if (!ASSERT_OK_PTR(skel, "btf_type_tag_user"))
-		goto free_vmlinux_btf;
+		goto cleanup;
 
 	bpf_program__set_autoload(skel->progs.test_user2, false);
 	bpf_program__set_autoload(skel->progs.test_user1, false);
@@ -124,7 +157,70 @@ static void test_btf_type_tag_vmlinux_user(void)
 
 	btf_type_tag_user__destroy(skel);
 
-free_vmlinux_btf:
+cleanup:
+	btf__free(vmlinux_btf);
+}
+
+static void test_btf_type_tag_mod_percpu(bool load_test_percpu1)
+{
+	struct btf *vmlinux_btf, *module_btf;
+	struct btf_type_tag_percpu *skel;
+	int err;
+
+	if (load_btfs(&vmlinux_btf, &module_btf, /*needs_vmlinux_tag=*/false))
+		return;
+
+	skel = btf_type_tag_percpu__open();
+	if (!ASSERT_OK_PTR(skel, "btf_type_tag_percpu"))
+		goto cleanup;
+
+	bpf_program__set_autoload(skel->progs.test_percpu_load, false);
+	bpf_program__set_autoload(skel->progs.test_percpu_helper, false);
+	if (load_test_percpu1)
+		bpf_program__set_autoload(skel->progs.test_percpu2, false);
+	else
+		bpf_program__set_autoload(skel->progs.test_percpu1, false);
+
+	err = btf_type_tag_percpu__load(skel);
+	ASSERT_ERR(err, "btf_type_tag_percpu");
+
+	btf_type_tag_percpu__destroy(skel);
+
+cleanup:
+	btf__free(module_btf);
+	btf__free(vmlinux_btf);
+}
+
+static void test_btf_type_tag_vmlinux_percpu(bool load_test)
+{
+	struct btf_type_tag_percpu *skel;
+	struct btf *vmlinux_btf = NULL;
+	int err;
+
+	if (load_btfs(&vmlinux_btf, NULL, /*needs_vmlinux_tag=*/true))
+		return;
+
+	skel = btf_type_tag_percpu__open();
+	if (!ASSERT_OK_PTR(skel, "btf_type_tag_percpu"))
+		goto cleanup;
+
+	bpf_program__set_autoload(skel->progs.test_percpu2, false);
+	bpf_program__set_autoload(skel->progs.test_percpu1, false);
+	if (load_test) {
+		bpf_program__set_autoload(skel->progs.test_percpu_helper, false);
+
+		err = btf_type_tag_percpu__load(skel);
+		ASSERT_ERR(err, "btf_type_tag_percpu_load");
+	} else {
+		bpf_program__set_autoload(skel->progs.test_percpu_load, false);
+
+		err = btf_type_tag_percpu__load(skel);
+		ASSERT_OK(err, "btf_type_tag_percpu_helper");
+	}
+
+	btf_type_tag_percpu__destroy(skel);
+
+cleanup:
 	btf__free(vmlinux_btf);
 }
 
@@ -134,10 +230,20 @@ void test_btf_tag(void)
 		test_btf_decl_tag();
 	if (test__start_subtest("btf_type_tag"))
 		test_btf_type_tag();
+
 	if (test__start_subtest("btf_type_tag_user_mod1"))
 		test_btf_type_tag_mod_user(true);
 	if (test__start_subtest("btf_type_tag_user_mod2"))
 		test_btf_type_tag_mod_user(false);
 	if (test__start_subtest("btf_type_tag_sys_user_vmlinux"))
 		test_btf_type_tag_vmlinux_user();
+
+	if (test__start_subtest("btf_type_tag_percpu_mod1"))
+		test_btf_type_tag_mod_percpu(true);
+	if (test__start_subtest("btf_type_tag_percpu_mod2"))
+		test_btf_type_tag_mod_percpu(false);
+	if (test__start_subtest("btf_type_tag_percpu_vmlinux_load"))
+		test_btf_type_tag_vmlinux_percpu(true);
+	if (test__start_subtest("btf_type_tag_percpu_vmlinux_helper"))
+		test_btf_type_tag_vmlinux_percpu(false);
 }

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

@@ -0,0 +1,66 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2022 Google */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+struct bpf_testmod_btf_type_tag_1 {
+	int a;
+};
+
+struct bpf_testmod_btf_type_tag_2 {
+	struct bpf_testmod_btf_type_tag_1 *p;
+};
+
+__u64 g;
+
+SEC("fentry/bpf_testmod_test_btf_type_tag_percpu_1")
+int BPF_PROG(test_percpu1, struct bpf_testmod_btf_type_tag_1 *arg)
+{
+	g = arg->a;
+	return 0;
+}
+
+SEC("fentry/bpf_testmod_test_btf_type_tag_percpu_2")
+int BPF_PROG(test_percpu2, struct bpf_testmod_btf_type_tag_2 *arg)
+{
+	g = arg->p->a;
+	return 0;
+}
+
+/* trace_cgroup_mkdir(struct cgroup *cgrp, const char *path)
+ *
+ * struct cgroup_rstat_cpu {
+ *   ...
+ *   struct cgroup *updated_children;
+ *   ...
+ * };
+ *
+ * struct cgroup {
+ *   ...
+ *   struct cgroup_rstat_cpu __percpu *rstat_cpu;
+ *   ...
+ * };
+ */
+SEC("tp_btf/cgroup_mkdir")
+int BPF_PROG(test_percpu_load, struct cgroup *cgrp, const char *path)
+{
+	g = (__u64)cgrp->rstat_cpu->updated_children;
+	return 0;
+}
+
+SEC("tp_btf/cgroup_mkdir")
+int BPF_PROG(test_percpu_helper, struct cgroup *cgrp, const char *path)
+{
+	struct cgroup_rstat_cpu *rstat;
+	__u32 cpu;
+
+	cpu = bpf_get_smp_processor_id();
+	rstat = (struct cgroup_rstat_cpu *)bpf_per_cpu_ptr(cgrp->rstat_cpu, cpu);
+	if (rstat) {
+		/* READ_ONCE */
+		*(volatile int *)rstat;
+	}
+
+	return 0;
+}