[PATCH bpf-next v2 0/2] bpf: Fix WARNING in bpf_trampoline_multi_detach

[PATCH bpf-next v2 0/2] bpf: Fix WARNING in bpf_trampoline_multi_detach

[Leon Hwang]

Since tracing_multi link does not set ftrace_managed, it would fail to
release the tracing_multi link when attaching tracing_multi link and
then attaching fentry link.

[    3.714215] WARNING: kernel/bpf/trampoline.c:1727 at bpf_trampoline_multi_detach+0x20b/0x240, CPU#1: test_progs/97
...
[    3.733170]  bpf_tracing_multi_link_release+0x14/0x30
[    3.733890]  bpf_link_free+0x58/0x130
[    3.734414]  bpf_link_release+0x23/0x30

Fix it by setting 'ftrace_managed = true' in register_fentry_multi().

Note: the reason of targeting bpf-next tree is I'm planning to add
tracing_multi link support for bpf progs, that would rely on the fix and
have code conflict with the test.

Changes:
v1 -> v2:
* Collect Acked-by from Jiri, thanks.
* Check arg using tracing_multi_arg_check() in bpf prog in test.
  (per Sashiko)
* v1: https://lore.kernel.org/bpf/20260710144734.78203-1-leon.hwang@linux.dev/

Leon Hwang (2):
  bpf: Mark tracing_multi trampolines as ftrace managed
  selftests/bpf: Test fentry link after tracing_multi link

 kernel/bpf/trampoline.c                       |  1 +
 .../selftests/bpf/prog_tests/tracing_multi.c  | 69 +++++++++++++++++++
 .../progs/tracing_multi_intersect_attach.c    |  8 +++
 3 files changed, 78 insertions(+)

--
2.55.0

[PATCH bpf-next v2 1/2] bpf: Mark tracing_multi trampolines as ftrace managed

[Leon Hwang]

Since tracing_multi link does not set ftrace_managed, it would fail to
release the tracing_multi link when attaching tracing_multi link and
then attaching fentry link.

[    3.714215] WARNING: kernel/bpf/trampoline.c:1727 at bpf_trampoline_multi_detach+0x20b/0x240, CPU#1: test_progs/97
...
[    3.733170]  bpf_tracing_multi_link_release+0x14/0x30
[    3.733890]  bpf_link_free+0x58/0x130
[    3.734414]  bpf_link_release+0x23/0x30

Fix it by setting 'ftrace_managed = true' in register_fentry_multi().

Fixes: aef4dfa790b2 ("bpf: Add bpf_trampoline_multi_attach/detach functions")
Acked-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 kernel/bpf/trampoline.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/kernel/bpf/trampoline.c b/kernel/bpf/trampoline.c
index 1a721fc4bef5..6eadf64f7ec9 100644
--- a/kernel/bpf/trampoline.c
+++ b/kernel/bpf/trampoline.c
@@ -1536,6 +1536,7 @@ static int register_fentry_multi(struct bpf_trampoline *tr, struct bpf_tramp_ima
 	if (bpf_trampoline_use_jmp(tr->flags))
 		addr = ftrace_jmp_set(addr);
 
+	tr->func.ftrace_managed = true;
 	ftrace_hash_add(data->reg, data->entry, ip, addr);
 	tr->cur_image = im;
 	return 0;
-- 
2.55.0

[PATCH bpf-next v2 2/2] selftests/bpf: Test fentry link after tracing_multi link

[Leon Hwang]

Verify that there's no any issue to attach tracing_multi link, then attach
fentry link.

Assisted-by: Codex:gpt-5.6-sol
Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/tracing_multi.c  | 69 +++++++++++++++++++
 .../progs/tracing_multi_intersect_attach.c    |  8 +++
 2 files changed, 77 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
index f02ffc7f41d7..0aa9532a05cf 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
@@ -460,6 +460,73 @@ static void test_intersect(void)
 	tracing_multi_intersect__destroy(skel);
 }
 
+static void test_fentry_after_multi(void)
+{
+	static const char * const funcs[] = {
+		"bpf_fentry_test1",
+	};
+	struct bpf_link *fentry_link = NULL, *multi_link = NULL;
+	struct tracing_multi_intersect *skel = NULL;
+	LIBBPF_OPTS(bpf_tracing_multi_opts, opts);
+	LIBBPF_OPTS(bpf_test_run_opts, topts);
+	__u32 *ids = NULL;
+	int err;
+
+	skel = tracing_multi_intersect__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "tracing_multi_intersect__open_and_load"))
+		return;
+
+	skel->bss->pid = getpid();
+
+	ids = get_ids(funcs, ARRAY_SIZE(funcs), NULL);
+	if (!ASSERT_OK_PTR(ids, "get_ids"))
+		goto cleanup;
+
+	opts.ids = ids;
+	opts.cnt = ARRAY_SIZE(funcs);
+	multi_link = bpf_program__attach_tracing_multi(skel->progs.fentry_1, NULL, &opts);
+	if (!ASSERT_OK_PTR(multi_link, "attach_multi"))
+		goto cleanup;
+
+	fentry_link = bpf_program__attach(skel->progs.fentry);
+	if (!ASSERT_OK_PTR(fentry_link, "attach_fentry"))
+		goto cleanup;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
+	if (!ASSERT_OK(err, "test_run"))
+		goto cleanup;
+	ASSERT_EQ(skel->bss->test_result_fentry_1, 1, "multi_fentry");
+	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry");
+
+	err = bpf_link__destroy(fentry_link);
+	fentry_link = NULL;
+	if (!ASSERT_OK(err, "destroy_fentry"))
+		goto cleanup;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
+	if (!ASSERT_OK(err, "test_run_multi"))
+		goto cleanup;
+	ASSERT_EQ(skel->bss->test_result_fentry_1, 2, "multi_fentry_only");
+	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry_detached");
+
+	err = bpf_link__destroy(multi_link);
+	multi_link = NULL;
+	if (!ASSERT_OK(err, "destroy_multi"))
+		goto cleanup;
+
+	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
+	if (!ASSERT_OK(err, "test_run_detached"))
+		goto cleanup;
+	ASSERT_EQ(skel->bss->test_result_fentry_1, 2, "multi_fentry_detached");
+	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry_still_detached");
+
+cleanup:
+	bpf_link__destroy(fentry_link);
+	bpf_link__destroy(multi_link);
+	free(ids);
+	tracing_multi_intersect__destroy(skel);
+}
+
 static void test_session(void)
 {
 	LIBBPF_OPTS(bpf_test_run_opts, topts);
@@ -957,4 +1024,6 @@ void test_tracing_multi_test(void)
 	if (test__start_subtest("attach_api_fails"))
 		test_attach_api_fails();
 	RUN_TESTS(tracing_multi_verifier);
+	if (test__start_subtest("fentry_after_multi"))
+		test_fentry_after_multi();
 }
diff --git a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
index cd5be0bb6ffd..5b0af8f4c62f 100644
--- a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
+++ b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
@@ -11,6 +11,14 @@ __u64 test_result_fentry_1 = 0;
 __u64 test_result_fentry_2 = 0;
 __u64 test_result_fexit_1 = 0;
 __u64 test_result_fexit_2 = 0;
+__u64 test_result_fentry = 0;
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(fentry)
+{
+	tracing_multi_arg_check(ctx, &test_result_fentry, false);
+	return 0;
+}
 
 SEC("fentry.multi")
 int BPF_PROG(fentry_1)
-- 
2.55.0

Re: [PATCH bpf-next v2 2/2] selftests/bpf: Test fentry link after tracing_multi link

[Jiri Olsa]

On Sat, Jul 11, 2026 at 08:48:22PM +0800, Leon Hwang wrote:
> Verify that there's no any issue to attach tracing_multi link, then attach
> fentry link.
> 
> Assisted-by: Codex:gpt-5.6-sol
> Signed-off-by: Leon Hwang <leon.hwang@linux.dev>

Acked-by: Jiri Olsa <jolsa@kernel.org>

thanks,
jirka


> ---
>  .../selftests/bpf/prog_tests/tracing_multi.c  | 69 +++++++++++++++++++
>  .../progs/tracing_multi_intersect_attach.c    |  8 +++
>  2 files changed, 77 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> index f02ffc7f41d7..0aa9532a05cf 100644
> --- a/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> +++ b/tools/testing/selftests/bpf/prog_tests/tracing_multi.c
> @@ -460,6 +460,73 @@ static void test_intersect(void)
>  	tracing_multi_intersect__destroy(skel);
>  }
>  
> +static void test_fentry_after_multi(void)
> +{
> +	static const char * const funcs[] = {
> +		"bpf_fentry_test1",
> +	};
> +	struct bpf_link *fentry_link = NULL, *multi_link = NULL;
> +	struct tracing_multi_intersect *skel = NULL;
> +	LIBBPF_OPTS(bpf_tracing_multi_opts, opts);
> +	LIBBPF_OPTS(bpf_test_run_opts, topts);
> +	__u32 *ids = NULL;
> +	int err;
> +
> +	skel = tracing_multi_intersect__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "tracing_multi_intersect__open_and_load"))
> +		return;
> +
> +	skel->bss->pid = getpid();
> +
> +	ids = get_ids(funcs, ARRAY_SIZE(funcs), NULL);
> +	if (!ASSERT_OK_PTR(ids, "get_ids"))
> +		goto cleanup;
> +
> +	opts.ids = ids;
> +	opts.cnt = ARRAY_SIZE(funcs);
> +	multi_link = bpf_program__attach_tracing_multi(skel->progs.fentry_1, NULL, &opts);
> +	if (!ASSERT_OK_PTR(multi_link, "attach_multi"))
> +		goto cleanup;
> +
> +	fentry_link = bpf_program__attach(skel->progs.fentry);
> +	if (!ASSERT_OK_PTR(fentry_link, "attach_fentry"))
> +		goto cleanup;
> +
> +	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
> +	if (!ASSERT_OK(err, "test_run"))
> +		goto cleanup;
> +	ASSERT_EQ(skel->bss->test_result_fentry_1, 1, "multi_fentry");
> +	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry");
> +
> +	err = bpf_link__destroy(fentry_link);
> +	fentry_link = NULL;
> +	if (!ASSERT_OK(err, "destroy_fentry"))
> +		goto cleanup;
> +
> +	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
> +	if (!ASSERT_OK(err, "test_run_multi"))
> +		goto cleanup;
> +	ASSERT_EQ(skel->bss->test_result_fentry_1, 2, "multi_fentry_only");
> +	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry_detached");
> +
> +	err = bpf_link__destroy(multi_link);
> +	multi_link = NULL;
> +	if (!ASSERT_OK(err, "destroy_multi"))
> +		goto cleanup;
> +
> +	err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry_1), &topts);
> +	if (!ASSERT_OK(err, "test_run_detached"))
> +		goto cleanup;
> +	ASSERT_EQ(skel->bss->test_result_fentry_1, 2, "multi_fentry_detached");
> +	ASSERT_EQ(skel->bss->test_result_fentry, 1, "fentry_still_detached");
> +
> +cleanup:
> +	bpf_link__destroy(fentry_link);
> +	bpf_link__destroy(multi_link);
> +	free(ids);
> +	tracing_multi_intersect__destroy(skel);
> +}
> +
>  static void test_session(void)
>  {
>  	LIBBPF_OPTS(bpf_test_run_opts, topts);
> @@ -957,4 +1024,6 @@ void test_tracing_multi_test(void)
>  	if (test__start_subtest("attach_api_fails"))
>  		test_attach_api_fails();
>  	RUN_TESTS(tracing_multi_verifier);
> +	if (test__start_subtest("fentry_after_multi"))
> +		test_fentry_after_multi();
>  }
> diff --git a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
> index cd5be0bb6ffd..5b0af8f4c62f 100644
> --- a/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
> +++ b/tools/testing/selftests/bpf/progs/tracing_multi_intersect_attach.c
> @@ -11,6 +11,14 @@ __u64 test_result_fentry_1 = 0;
>  __u64 test_result_fentry_2 = 0;
>  __u64 test_result_fexit_1 = 0;
>  __u64 test_result_fexit_2 = 0;
> +__u64 test_result_fentry = 0;
> +
> +SEC("fentry/bpf_fentry_test1")
> +int BPF_PROG(fentry)
> +{
> +	tracing_multi_arg_check(ctx, &test_result_fentry, false);
> +	return 0;
> +}
>  
>  SEC("fentry.multi")
>  int BPF_PROG(fentry_1)
> -- 
> 2.55.0
> 

Re: [PATCH bpf-next v2 0/2] bpf: Fix WARNING in bpf_trampoline_multi_detach

[patchwork-bot+netdevbpf]

Hello:

This series was applied to bpf/bpf-next.git (master)
by Kumar Kartikeya Dwivedi <memxor@gmail.com>:

On Sat, 11 Jul 2026 20:48:20 +0800 you wrote:
> Since tracing_multi link does not set ftrace_managed, it would fail to
> release the tracing_multi link when attaching tracing_multi link and
> then attaching fentry link.
> 
> [    3.714215] WARNING: kernel/bpf/trampoline.c:1727 at bpf_trampoline_multi_detach+0x20b/0x240, CPU#1: test_progs/97
> ...
> [    3.733170]  bpf_tracing_multi_link_release+0x14/0x30
> [    3.733890]  bpf_link_free+0x58/0x130
> [    3.734414]  bpf_link_release+0x23/0x30
> 
> [...]

Here is the summary with links:
  - [bpf-next,v2,1/2] bpf: Mark tracing_multi trampolines as ftrace managed
    https://git.kernel.org/bpf/bpf-next/c/30bdd6d1384d
  - [bpf-next,v2,2/2] selftests/bpf: Test fentry link after tracing_multi link
    https://git.kernel.org/bpf/bpf-next/c/539d3edf8e53

You are awesome, thank you!
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