Re: [PATCH bpf v3 2/2] selftests/bpf: Add test to ensure kprobe_multi is not sleepable

Leon Hwang
2026-04-02T04:14:12Z

Above all, I think the test should reproduce the BUG without the fix.

I update the test to reproduce the BUG, then verify that the BUG will be
rejected with the fix.

The updated test is attached at last.

On 2/4/26 03:11, Varun R Mallya wrote:
> Add a selftest to ensure that kprobe_multi programs cannot be attached
> using the BPF_F_SLEEPABLE flag. This test succeeds when the kernel
> rejects attachment of kprobe_multi when the BPF_F_SLEEPABLE flag is set.
>
> Signed-off-by: Varun R Mallya <varunrmallya@gmail.com>
> ---
> .../bpf/prog_tests/kprobe_multi_test.c | 41 +++++++++++++++++++
> .../bpf/progs/kprobe_multi_sleepable.c | 13 ++++++
> 2 files changed, 54 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> index 78c974d4ea33..f02fec2b6fda 100644
> --- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> +++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
> @@ -10,6 +10,7 @@
> #include "kprobe_multi_session_cookie.skel.h"
> #include "kprobe_multi_verifier.skel.h"
> #include "kprobe_write_ctx.skel.h"
> +#include "kprobe_multi_sleepable.skel.h"
> #include "bpf/libbpf_internal.h"
> #include "bpf/hashmap.h"
>
> @@ -633,6 +634,44 @@ static void test_attach_write_ctx(void)
> }
> #endif
>
> +static void test_attach_multi_sleepable(void)
> +{
> + struct kprobe_multi_sleepable *skel;
> + int err;
> +
> + skel = kprobe_multi_sleepable__open();
> + if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open"))
> + return;
> +
> + err = bpf_program__set_flags(skel->progs.handle_kprobe_multi_sleepable,
> + BPF_F_SLEEPABLE);
> + if (!ASSERT_OK(err, "bpf_program__set_flags"))
> + goto cleanup;
> +
> + /* Load should succeed even with BPF_F_SLEEPABLE for KPROBE types */
> + err = kprobe_multi_sleepable__load(skel);
> + if (!ASSERT_OK(err, "kprobe_multi_sleepable__load"))
> + goto cleanup;
> +
> + /* Attachment must fail for kprobe.multi + BPF_F_SLEEPABLE.
> + * Also chosen a stable symbol to send into opts
> + */
> + LIBBPF_OPTS(bpf_kprobe_multi_opts, opts);
> + const char *sym = "vfs_read";

They should stay with skel and err. See below.

> +
> + opts.syms = &sym;
> + opts.cnt = 1;
> +
> + skel->links.handle_kprobe_multi_sleepable =
> + bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable,
> + NULL, &opts);
> + ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable,
> + "bpf_program__attach_kprobe_multi_opts");

As Kumar suggested, better to also verify the error here.

ASSERT_EQ(libbpf_get_error(skel->links.handle_kprobe_multi_sleepable),
-EINVAL,
"bpf_program__attach_kprobe_multi_opts error");

> +
> +cleanup:
> + kprobe_multi_sleepable__destroy(skel);
> +}
> +

[...]

Thanks,
Leon

---

diff --git a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
index 78c974d4ea33..d59cf840da83 100644
--- a/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/kprobe_multi_test.c
@@ -10,6 +10,7 @@
#include "kprobe_multi_session_cookie.skel.h"
#include "kprobe_multi_verifier.skel.h"
#include "kprobe_write_ctx.skel.h"
+#include "kprobe_multi_sleepable.skel.h"
#include "bpf/libbpf_internal.h"
#include "bpf/hashmap.h"

@@ -633,6 +634,52 @@ static void test_attach_write_ctx(void)
}
#endif

+static void test_attach_multi_sleepable(void)
+{
+ struct kprobe_multi_sleepable *skel;
+ const char *sym = "bpf_fentry_test1";
+ int err;
+ LIBBPF_OPTS(bpf_test_run_opts, topts);
+ LIBBPF_OPTS(bpf_kprobe_multi_opts, opts,
+ .syms = &sym,
+ .cnt = 1
+ );
+
+ skel = kprobe_multi_sleepable__open();
+ if (!ASSERT_OK_PTR(skel, "kprobe_multi_sleepable__open"))
+ return;
+
+ skel->bss->user_ptr = skel;
+
+ err =
bpf_program__set_flags(skel->progs.handle_kprobe_multi_sleepable,
+ BPF_F_SLEEPABLE);
+ if (!ASSERT_OK(err, "bpf_program__set_flags"))
+ goto cleanup;
+
+ /* Load should succeed even with BPF_F_SLEEPABLE for KPROBE types */
+ err = kprobe_multi_sleepable__load(skel);
+ if (!ASSERT_OK(err, "kprobe_multi_sleepable__load"))
+ goto cleanup;
+
+ /*
+ * Attachment must fail for kprobe.multi + BPF_F_SLEEPABLE.
+ * Also chosen a stable symbol to send into opts
+ */
+ skel->links.handle_kprobe_multi_sleepable =
+
bpf_program__attach_kprobe_multi_opts(skel->progs.handle_kprobe_multi_sleepable,
+ NULL, &opts);
+ ASSERT_ERR_PTR(skel->links.handle_kprobe_multi_sleepable,
+ "bpf_program__attach_kprobe_multi_opts");
+
ASSERT_EQ(libbpf_get_error(skel->links.handle_kprobe_multi_sleepable),
-EINVAL,
+ "attach_multi_sleepable_err");
+
+ err =
bpf_prog_test_run_opts(bpf_program__fd(skel->progs.fentry), &topts);
+ ASSERT_OK(err, "bpf_prog_test_run_opts");
+
+cleanup:
+ kprobe_multi_sleepable__destroy(skel);
+}
+
void serial_test_kprobe_multi_bench_attach(void)
{
if (test__start_subtest("kernel"))
@@ -676,5 +723,7 @@ void test_kprobe_multi_test(void)
test_unique_match();
if (test__start_subtest("attach_write_ctx"))
test_attach_write_ctx();
+ if (test__start_subtest("attach_multi_sleepable"))
+ test_attach_multi_sleepable();
RUN_TESTS(kprobe_multi_verifier);
}
diff --git a/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
new file mode 100644
index 000000000000..932e1d9c72e2
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/kprobe_multi_sleepable.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+void *user_ptr = 0;
+
+SEC("kprobe.multi")
+int handle_kprobe_multi_sleepable(struct pt_regs *ctx)
+{
+ int a, err;
+
+ err = bpf_copy_from_user(&a, sizeof(a), user_ptr);
+ barrier_var(a);
+ return err;
+}
+
+SEC("fentry/bpf_fentry_test1")
+int BPF_PROG(fentry)
+{
+ return 0;
+}
+
+char _license[] SEC("license") = "GPL";