On Fri, Mar 20, 2026 at 10:01 PM Mykyta Yatsenko
<[email protected]> wrote:
>
> Sun Jian <[email protected]> writes:
>
> > trampoline_count fills all trampoline attachment slots for a single
> > target function and verifies that one extra attach fails with -E2BIG.
> >
> > It currently targets bpf_modify_return_test, which is also used by
> > other selftests such as modify_return, get_func_ip_test, and
> > get_func_args_test. When such tests run in parallel, they can contend
> > for the same per-function trampoline quota and cause unexpected attach
> > failures. This issue is currently masked by harness serialization.
> >
> > Move trampoline_count to a dedicated bpf_testmod target and register it
> > for fmod_ret attachment. Also route the final trigger through
> > trigger_module_test_read, so the execution path exercises the same
> > dedicated target.
> >
> > This keeps the test semantics unchanged while isolating it from other
> > selftests, so it no longer needs to run in serial mode. Remove the
> > TODO comment as well.
> Is it really worth it just for ditching serial mode, does it improve
> test_progs speed? Either way it's worth adding a comment for
> bpf_testmod_trampoline_count_test() explaining that no other test should
> attempt attaching to it.
The main point here is not to speed up test_progs. The trampoline
count limit is a
per-func, system-wide quota. The purpose of this change is to avoid
contention with
other selftests attaching to the same target function. Allowing this
test to run in parallel
is just a consequence, not the goal, as the TODO comment already indicated.
Adding a short comment is not a bad idea, but
bpf_testmod_trampoline_count_test()
is already fairly self-descriptive.
> >
> > Tested:
> > ./test_progs -t trampoline_count -vv
> > ./test_progs -t modify_return -vv
> > ./test_progs -t get_func_ip_test -vv
> > ./test_progs -t get_func_args_test -vv
> > ./test_progs -j$(nproc) -t trampoline_count -vv
> > ./test_progs -j$(nproc) -t
> > trampoline_count,modify_return,get_func_ip_test,get_func_args_test,\
> > kprobe_multi_test -vv
> > 20 runs of:
> > ./test_progs -j$(nproc) -t
> > trampoline_count,modify_return,get_func_ip_test,get_func_args_test,\
> > kprobe_multi_test
> >
> > Suggested-by: Jiri Olsa <[email protected]>
> > Signed-off-by: Sun Jian <[email protected]>
> > ---
> > Link:https://lore.kernel.org/bpf/[email protected]/T/#m6253b7fe96fe1a4df65b274c95aac786598a9857
> >
> > v3:
> > - route the final trigger through trigger_module_test_read() and make
> > bpf_testmod_test_read() call the dedicated trampoline_count target,
> > as suggested by Jiri
> >
> > v2:
> > - rewrite the subject to describe the change
> > - resend with the correct patch content
> >
> > .../bpf/prog_tests/trampoline_count.c | 17 ++++----------
> > .../bpf/progs/test_trampoline_count.c | 6 ++---
> > .../selftests/bpf/test_kmods/bpf_testmod.c | 23 +++++++++++++++++++
> > 3 files changed, 30 insertions(+), 16 deletions(-)
> >
> > diff --git a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> > b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> > index 6cd7349d4a2b..dd2e5c84a4b5 100644
> > --- a/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> > +++ b/tools/testing/selftests/bpf/prog_tests/trampoline_count.c
> > @@ -30,16 +30,14 @@ static struct bpf_program *load_prog(char *file, char
> > *name, struct inst *inst)
> > return prog;
> > }
> >
> > -/* TODO: use different target function to run in concurrent mode */
> > -void serial_test_trampoline_count(void)
> > +void test_trampoline_count(void)
> > {
> > char *file = "test_trampoline_count.bpf.o";
> > char *const progs[] = { "fentry_test", "fmod_ret_test", "fexit_test"
> > };
> > - int bpf_max_tramp_links, err, i, prog_fd;
> > + int bpf_max_tramp_links, i;
> > struct bpf_program *prog;
> > struct bpf_link *link;
> > struct inst *inst;
> > - LIBBPF_OPTS(bpf_test_run_opts, opts);
> >
> > bpf_max_tramp_links = get_bpf_max_tramp_links();
> > if (!ASSERT_GE(bpf_max_tramp_links, 1, "bpf_max_tramp_links"))
> > @@ -80,17 +78,10 @@ void serial_test_trampoline_count(void)
> > goto cleanup;
> >
> > /* and finally execute the probe */
> > - prog_fd = bpf_program__fd(prog);
> > - if (!ASSERT_GE(prog_fd, 0, "bpf_program__fd"))
> > + if (!ASSERT_OK(trigger_module_test_read(256),
> > + "trigger_module_test_read"))
> > goto cleanup;
> >
> > - err = bpf_prog_test_run_opts(prog_fd, &opts);
> > - if (!ASSERT_OK(err, "bpf_prog_test_run_opts"))
> > - goto cleanup;
> > -
> > - ASSERT_EQ(opts.retval & 0xffff, 33, "bpf_modify_return_test.result");
> > - ASSERT_EQ(opts.retval >> 16, 2, "bpf_modify_return_test.side_effect");
> > -
> > cleanup:
> > for (; i >= 0; i--) {
> > bpf_link__destroy(inst[i].link);
> > diff --git a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> > b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> > index 7765720da7d5..14ad2f53cf33 100644
> > --- a/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> > +++ b/tools/testing/selftests/bpf/progs/test_trampoline_count.c
> > @@ -3,19 +3,19 @@
> > #include <bpf/bpf_helpers.h>
> > #include <bpf/bpf_tracing.h>
> >
> > -SEC("fentry/bpf_modify_return_test")
> > +SEC("fentry/bpf_testmod_trampoline_count_test")
> > int BPF_PROG(fentry_test, int a, int *b)
> > {
> > return 0;
> > }
> >
> > -SEC("fmod_ret/bpf_modify_return_test")
> > +SEC("fmod_ret/bpf_testmod_trampoline_count_test")
> > int BPF_PROG(fmod_ret_test, int a, int *b, int ret)
> > {
> > return 0;
> > }
> >
> > -SEC("fexit/bpf_modify_return_test")
> > +SEC("fexit/bpf_testmod_trampoline_count_test")
> > int BPF_PROG(fexit_test, int a, int *b, int ret)
> > {
> > return 0;
> > diff --git a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > index e62c6b78657f..47583577e021 100644
> > --- a/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > +++ b/tools/testing/selftests/bpf/test_kmods/bpf_testmod.c
> > @@ -470,6 +470,8 @@ noinline void bpf_testmod_stacktrace_test_1(void)
> >
> > int bpf_testmod_fentry_ok;
> >
> > +noinline int bpf_testmod_trampoline_count_test(int a, int *b);
> > +
> > noinline ssize_t
> > bpf_testmod_test_read(struct file *file, struct kobject *kobj,
> > const struct bin_attribute *bin_attr,
> > @@ -548,6 +550,10 @@ bpf_testmod_test_read(struct file *file, struct
> > kobject *kobj,
> > 21, 22, 23, 24, 25, 26) != 231)
> > goto out;
> >
> > + i = 2;
> > + if (bpf_testmod_trampoline_count_test(1, &i) != 4 || i != 3)
> > + goto out;
> > +
> Do we need to add this test for the bpf_testmod_trampoline_count_test(),
> if it's supposed to be used only for the trampoline count test, which
> probably does not care what function actually does internally.
This part was only added to keep the execution path conceptually aligned
with the dedicated target change. As for this and the above comment suggestion,
I'm fine leaving both to maintainer preference.
Sun Jian
> > bpf_testmod_stacktrace_test_1();
> >
> > bpf_testmod_fentry_ok = 1;
> > @@ -581,6 +587,12 @@ noinline int bpf_fentry_shadow_test(int a)
> > }
> > EXPORT_SYMBOL_GPL(bpf_fentry_shadow_test);
> >
> > +noinline int bpf_testmod_trampoline_count_test(int a, int *b)
> > +{
> > + *b += 1;
> > + return a + *b;
> > +}
> > +
> > __bpf_hook_end();
> >
> > static struct bin_attribute bin_attr_bpf_testmod_file __ro_after_init = {
> > @@ -1843,6 +1855,16 @@ struct bpf_struct_ops testmod_multi_st_ops = {
> >
> > extern int bpf_fentry_test1(int a);
> >
> > +BTF_KFUNCS_START(bpf_testmod_trampoline_count_ids)
> > +BTF_ID_FLAGS(func, bpf_testmod_trampoline_count_test)
> > +BTF_KFUNCS_END(bpf_testmod_trampoline_count_ids)
> > +
> > +static const struct
> > +btf_kfunc_id_set bpf_testmod_trampoline_count_fmodret_set = {
> > + .owner = THIS_MODULE,
> > + .set = &bpf_testmod_trampoline_count_ids,
> > +};
> > +
> > static int bpf_testmod_init(void)
> > {
> > const struct btf_id_dtor_kfunc bpf_testmod_dtors[] = {
> > @@ -1859,6 +1881,7 @@ static int bpf_testmod_init(void)
> > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_TRACING,
> > &bpf_testmod_kfunc_set);
> > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_SYSCALL,
> > &bpf_testmod_kfunc_set);
> > ret = ret ?: register_btf_kfunc_id_set(BPF_PROG_TYPE_STRUCT_OPS,
> > &bpf_testmod_kfunc_set);
> > + ret = ret ?:
> > register_btf_fmodret_id_set(&bpf_testmod_trampoline_count_fmodret_set);
> > ret = ret ?: register_bpf_struct_ops(&bpf_bpf_testmod_ops,
> > bpf_testmod_ops);
> > ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops2,
> > bpf_testmod_ops2);
> > ret = ret ?: register_bpf_struct_ops(&bpf_testmod_ops3,
> > bpf_testmod_ops3);
> >
> > base-commit: 8a30aeb0d1b4e4aaf7f7bae72f20f2ae75385ccb
> > --
> > 2.43.0
