[PATCH bpf-next v2 7/9] libbpf: don't free btf if program of multi-link tracing existing

Menglong Dong
2024-03-11T09:35:22Z

By default, the kernel btf that we load during loading program will be
freed after the programs are loaded in bpf_object_load(). However, we
still need to use these btf for tracing of multi-link during attaching.
Therefore, we don't free the btfs until the bpf object is closed if any
bpf programs of the type multi-link tracing exist.

Meanwhile, introduce the new api bpf_object__free_btf() to manually free
the btfs after attaching.

Signed-off-by: Menglong Dong <dongmenglong.8@bytedance.com>
---
tools/lib/bpf/libbpf.c | 47 ++++++++++++++++++++++++++++++----------
tools/lib/bpf/libbpf.h | 2 ++
tools/lib/bpf/libbpf.map | 1 +
3 files changed, 38 insertions(+), 12 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 567ad367e7aa..fd5428494a7e 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8267,6 +8267,39 @@ static int bpf_object_prepare_struct_ops(struct bpf_object *obj)
return 0;
}

+void bpf_object__free_btfs(struct bpf_object *obj)
+{
+ int i;
+
+ /* clean up module BTFs */
+ for (i = 0; i < obj->btf_module_cnt; i++) {
+ close(obj->btf_modules[i].fd);
+ btf__free(obj->btf_modules[i].btf);
+ free(obj->btf_modules[i].name);
+ }
+ free(obj->btf_modules);
+ obj->btf_modules = NULL;
+ obj->btf_module_cnt = 0;
+
+ /* clean up vmlinux BTF */
+ btf__free(obj->btf_vmlinux);
+ obj->btf_vmlinux = NULL;
+}
+
+static void bpf_object_early_free_btf(struct bpf_object *obj)
+{
+ struct bpf_program *prog;
+
+ bpf_object__for_each_program(prog, obj) {
+ if (prog->expected_attach_type == BPF_TRACE_FENTRY_MULTI ||
+ prog->expected_attach_type == BPF_TRACE_FEXIT_MULTI ||
+ prog->expected_attach_type == BPF_MODIFY_RETURN_MULTI)
+ return;
+ }
+
+ bpf_object__free_btfs(obj);
+}
+
static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const char *target_btf_path)
{
int err, i;
@@ -8307,18 +8340,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
/* clean up fd_array */
zfree(&obj->fd_array);

- /* clean up module BTFs */
- for (i = 0; i < obj->btf_module_cnt; i++) {
- close(obj->btf_modules[i].fd);
- btf__free(obj->btf_modules[i].btf);
- free(obj->btf_modules[i].name);
- }
- free(obj->btf_modules);
-
- /* clean up vmlinux BTF */
- btf__free(obj->btf_vmlinux);
- obj->btf_vmlinux = NULL;
-
+ bpf_object_early_free_btf(obj);
obj->loaded = true; /* doesn't matter if successfully or not */

if (err)
@@ -8791,6 +8813,7 @@ void bpf_object__close(struct bpf_object *obj)
usdt_manager_free(obj->usdt_man);
obj->usdt_man = NULL;

+ bpf_object__free_btfs(obj);
bpf_gen__free(obj->gen_loader);
bpf_object__elf_finish(obj);
bpf_object_unload(obj);
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index 5723cbbfcc41..c41a909ea4c1 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -299,6 +299,8 @@ LIBBPF_API struct bpf_program *
bpf_object__find_program_by_name(const struct bpf_object *obj,
const char *name);

+LIBBPF_API void bpf_object__free_btfs(struct bpf_object *obj);
+
LIBBPF_API int
libbpf_prog_type_by_name(const char *name, enum bpf_prog_type *prog_type,
enum bpf_attach_type *expected_attach_type);
diff --git a/tools/lib/bpf/libbpf.map b/tools/lib/bpf/libbpf.map
index 86804fd90dd1..57642b78917f 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -413,4 +413,5 @@ LIBBPF_1.4.0 {
bpf_token_create;
btf__new_split;
btf_ext__raw_data;
+ bpf_object__free_btfs;
} LIBBPF_1.3.0;
--
2.39.2