linux-kernel - [PATCH bpf-next v2 12/18] libbpf: don't free btf if tracing

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Message-Id: <20250703121521.1874196-13-dongml2@chinatelecom.cn>
Date: Thu,  3 Jul 2025 20:15:15 +0800
From: Menglong Dong <menglong8.dong@...il.com>
To: alexei.starovoitov@...il.com,
	rostedt@...dmis.org,
	jolsa@...nel.org
Cc: bpf@...r.kernel.org,
	Menglong Dong <dongml2@...natelecom.cn>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>,
	Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	John Fastabend <john.fastabend@...il.com>,
	KP Singh <kpsingh@...nel.org>,
	Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH bpf-next v2 12/18] libbpf: don't free btf if tracing_multi progs existing

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 <dongml2@...natelecom.cn>
---
 tools/lib/bpf/libbpf.c   | 24 +++++++++++++++++++++++-
 tools/lib/bpf/libbpf.h   |  2 ++
 tools/lib/bpf/libbpf.map |  1 +
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index aee36402f0a3..530c29f2f5fc 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -8583,6 +8583,28 @@ static void bpf_object_post_load_cleanup(struct bpf_object *obj)
 	obj->btf_vmlinux = NULL;
 }
 
+void bpf_object__free_btfs(struct bpf_object *obj)
+{
+	if (!obj->btf_vmlinux || obj->state != OBJ_LOADED)
+		return;
+
+	bpf_object_post_load_cleanup(obj);
+}
+
+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_post_load_cleanup(obj);
+}
+
 static int bpf_object_prepare(struct bpf_object *obj, const char *target_btf_path)
 {
 	int err;
@@ -8654,7 +8676,7 @@ static int bpf_object_load(struct bpf_object *obj, int extra_log_level, const ch
 			err = bpf_gen__finish(obj->gen_loader, obj->nr_programs, obj->nr_maps);
 	}
 
-	bpf_object_post_load_cleanup(obj);
+	bpf_object_early_free_btf(obj);
 	obj->state = OBJ_LOADED; /* doesn't matter if successfully or not */
 
 	if (err) {
diff --git a/tools/lib/bpf/libbpf.h b/tools/lib/bpf/libbpf.h
index d1cf813a057b..7cc810aa7967 100644
--- a/tools/lib/bpf/libbpf.h
+++ b/tools/lib/bpf/libbpf.h
@@ -323,6 +323,8 @@ 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 c7fc0bde5648..4a0c993221a5 100644
--- a/tools/lib/bpf/libbpf.map
+++ b/tools/lib/bpf/libbpf.map
@@ -444,4 +444,5 @@ LIBBPF_1.6.0 {
 		bpf_program__line_info_cnt;
 		btf__add_decl_attr;
 		btf__add_type_attr;
+		bpf_object__free_btfs;
 } LIBBPF_1.5.0;
-- 
2.39.5