Re: [PATCH bpf 5/5] selftests/bpf: extend multi-uprobe tests with USDTs

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, May 20, 2024 at 09:54:40PM -0700, Andrii Nakryiko wrote:
> On Mon, May 20, 2024 at 4:47 PM Andrii Nakryiko <andrii@kernel.org> 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@kernel.org>
> > ---
> >  .../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.

tests are passing for me with the changes above

> 
> 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).

agreed, perhaps also the patch #3 for libbpf detection?

jirka