On Mon, May 20, 2024 at 4:47 PM Andrii Nakryiko <andrii@xxxxxxxxxx> wrote:
>
> Validate libbpf's USDT-over-multi-uprobe logic by adding USDTs to
> existing multi-uprobe tests. This checks correct libbpf fallback to
> singular uprobes (when run on older kernels with buggy PID filtering).
> We reuse already established child process and child thread testing
> infrastructure, so additions are minimal. These test fail on either
> older kernels or older version of libbpf that doesn't detect PID
> filtering problems.
>
> Signed-off-by: Andrii Nakryiko <andrii@xxxxxxxxxx>
> ---
> .../bpf/prog_tests/uprobe_multi_test.c | 22 +++++++++++++
> .../selftests/bpf/progs/uprobe_multi.c | 33 +++++++++++++++++--
> 2 files changed, 53 insertions(+), 2 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
> index 677232d31432..85d46e568e90 100644
> --- a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
> +++ b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
> @@ -8,6 +8,7 @@
> #include "uprobe_multi_usdt.skel.h"
> #include "bpf/libbpf_internal.h"
> #include "testing_helpers.h"
> +#include "../sdt.h"
>
> static char test_data[] = "test_data";
>
> @@ -26,6 +27,11 @@ noinline void uprobe_multi_func_3(void)
> asm volatile ("");
> }
>
> +noinline void usdt_trigger(void)
> +{
> + STAP_PROBE(test, pid_filter_usdt);
> +}
> +
> struct child {
> int go[2];
> int c2p[2]; /* child -> parent channel */
> @@ -269,8 +275,24 @@ __test_attach_api(const char *binary, const char *pattern, struct bpf_uprobe_mul
> if (!ASSERT_OK_PTR(skel->links.uprobe_extra, "bpf_program__attach_uprobe_multi"))
> goto cleanup;
>
> + /* Attach (uprobe-backed) USDTs */
> + skel->links.usdt_pid = bpf_program__attach_usdt(skel->progs.usdt_pid, pid, binary,
> + "test", "pid_filter_usdt", NULL);
> + if (!ASSERT_OK_PTR(skel->links.usdt_pid, "attach_usdt_pid"))
> + goto cleanup;
> +
> + skel->links.usdt_extra = bpf_program__attach_usdt(skel->progs.usdt_extra, -1, binary,
> + "test", "pid_filter_usdt", NULL);
> + if (!ASSERT_OK_PTR(skel->links.usdt_extra, "attach_usdt_extra"))
> + goto cleanup;
> +
> uprobe_multi_test_run(skel, child);
>
> + ASSERT_FALSE(skel->bss->bad_pid_seen_usdt, "bad_pid_seen_usdt");
> + if (child) {
> + ASSERT_EQ(skel->bss->child_pid_usdt, child->pid, "usdt_multi_child_pid");
> + ASSERT_EQ(skel->bss->child_tid_usdt, child->tid, "usdt_multi_child_tid");
> + }
> cleanup:
> uprobe_multi__destroy(skel);
> }
> diff --git a/tools/testing/selftests/bpf/progs/uprobe_multi.c b/tools/testing/selftests/bpf/progs/uprobe_multi.c
> index 86a7ff5d3726..44190efcdba2 100644
> --- a/tools/testing/selftests/bpf/progs/uprobe_multi.c
> +++ b/tools/testing/selftests/bpf/progs/uprobe_multi.c
> @@ -1,8 +1,8 @@
> // SPDX-License-Identifier: GPL-2.0
> -#include <linux/bpf.h>
> +#include "vmlinux.h"
> #include <bpf/bpf_helpers.h>
> #include <bpf/bpf_tracing.h>
> -#include <stdbool.h>
> +#include <bpf/usdt.bpf.h>
>
> char _license[] SEC("license") = "GPL";
>
> @@ -23,9 +23,12 @@ __u64 uprobe_multi_sleep_result = 0;
> int pid = 0;
> int child_pid = 0;
> int child_tid = 0;
> +int child_pid_usdt = 0;
> +int child_tid_usdt = 0;
>
> int expect_pid = 0;
> bool bad_pid_seen = false;
> +bool bad_pid_seen_usdt = false;
>
> bool test_cookie = false;
> void *user_ptr = 0;
> @@ -112,3 +115,29 @@ int uprobe_extra(struct pt_regs *ctx)
> /* we need this one just to mix PID-filtered and global uprobes */
> return 0;
> }
> +
> +SEC("usdt")
> +int usdt_pid(struct pt_regs *ctx)
> +{
> + __u64 cur_pid_tgid = bpf_get_current_pid_tgid();
> + __u32 cur_pid;
> +
> + cur_pid = cur_pid_tgid >> 32;
> + if (pid && cur_pid != pid)
> + return 0;
> +
> + if (expect_pid && cur_pid != expect_pid)
> + bad_pid_seen_usdt = true;
> +
> + child_pid_usdt = cur_pid_tgid >> 32;
> + child_tid_usdt = (__u32)cur_pid_tgid;
> +
> + return 0;
> +}
> +
> +SEC("usdt")
> +int usdt_extra(struct pt_regs *ctx)
> +{
> + /* we need this one just to mix PID-filtered and global USDT probes */
> + return 0;
> +}
> --
> 2.43.0
>
I lost the following during the final rebase before submitting,
sigh... With the piece below tests are passing again:
diff --git a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
index 85d46e568e90..bf6ca8e3eb13 100644
--- a/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
+++ b/tools/testing/selftests/bpf/prog_tests/uprobe_multi_test.c
@@ -96,6 +96,7 @@ static struct child *spawn_child(void)
uprobe_multi_func_1();
uprobe_multi_func_2();
uprobe_multi_func_3();
+ usdt_trigger();
exit(errno);
}
@@ -123,6 +124,7 @@ static void *child_thread(void *ctx)
uprobe_multi_func_1();
uprobe_multi_func_2();
uprobe_multi_func_3();
+ usdt_trigger();
err = 0;
pthread_exit(&err);
@@ -188,6 +190,7 @@ static void uprobe_multi_test_run(struct
uprobe_multi *skel, struct child *child
uprobe_multi_func_1();
uprobe_multi_func_2();
uprobe_multi_func_3();
+ usdt_trigger();
}
if (child)
I'll wait till tomorrow for any feedback and will post v2.
I'm also curious about logistics? Do we want to get everything through
the bpf tree? Or bpf-next? Or split somehow? Thoughts?
I think the fix in patch #1 is important enough to backport to stable
kernels (multi-uprobes went into upstream v6.6 kernel, FYI).
