Re: [PATCH v3 4/4] selftest/bpf: Test a perf bpf program that suppresses side effects.

[Song Liu]

On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@xxxxxxxxxxxx> wrote:
>
> The test sets a hardware breakpoint and uses a bpf program to suppress the
> side effects of a perf event sample, including I/O availability signals,
> SIGTRAPs, and decrementing the event counter limit, if the ip matches the
> expected value. Then the function with the breakpoint is executed multiple
> times to test that all effects behave as expected.
>
> Signed-off-by: Kyle Huey <khuey@xxxxxxxxxxxx>
> ---
>  .../selftests/bpf/prog_tests/perf_skip.c      | 140 ++++++++++++++++++
>  .../selftests/bpf/progs/test_perf_skip.c      |  15 ++
>  2 files changed, 155 insertions(+)
>  create mode 100644 tools/testing/selftests/bpf/prog_tests/perf_skip.c
>  create mode 100644 tools/testing/selftests/bpf/progs/test_perf_skip.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/perf_skip.c b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> new file mode 100644
> index 000000000000..0200736a8baf
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> @@ -0,0 +1,140 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#define _GNU_SOURCE
> +
> +#include <test_progs.h>
> +#include "test_perf_skip.skel.h"
> +#include <linux/compiler.h>
> +#include <linux/hw_breakpoint.h>
> +#include <sys/mman.h>
> +
> +#ifndef TRAP_PERF
> +#define TRAP_PERF 6
> +#endif
> +
> +int signals_unexpected = 1;
> +int sigio_count, sigtrap_count;
> +
> +static void handle_sigio(int sig __always_unused)
> +{
> +       ASSERT_OK(signals_unexpected, "perf event not skipped");

ASSERT_OK is a little confusing. Maybe do something like:

static int signals_expected;
static void handle_sigio(int sig __always_unused)
{
    ASSERT_EQ(signals_expected, 1, "expected sig_io");
}
serial_test_perf_skip()
{
...
signals_expected = 1;
}

> +       ++sigio_count;
> +}
> +
> +static void handle_sigtrap(int signum __always_unused,
> +                          siginfo_t *info,
> +                          void *ucontext __always_unused)
> +{
> +       ASSERT_OK(signals_unexpected, "perf event not skipped");
ditto

> +       ASSERT_EQ(info->si_code, TRAP_PERF, "wrong si_code");
> +       ++sigtrap_count;
> +}
> +
> +static noinline int test_function(void)
> +{
> +       asm volatile ("");
> +       return 0;
> +}
> +
> +void serial_test_perf_skip(void)
> +{
> +       struct sigaction action = {};
> +       struct sigaction previous_sigtrap;
> +       sighandler_t previous_sigio;
> +       struct test_perf_skip *skel = NULL;
> +       struct perf_event_attr attr = {};
> +       int perf_fd = -1;
> +       int err;
> +       struct f_owner_ex owner;
> +       struct bpf_link *prog_link = NULL;
> +
> +       action.sa_flags = SA_SIGINFO | SA_NODEFER;
> +       action.sa_sigaction = handle_sigtrap;
> +       sigemptyset(&action.sa_mask);
> +       if (!ASSERT_OK(sigaction(SIGTRAP, &action, &previous_sigtrap), "sigaction"))
> +               return;
> +
> +       previous_sigio = signal(SIGIO, handle_sigio);

handle signal() errors here?

> +
> +       skel = test_perf_skip__open_and_load();
> +       if (!ASSERT_OK_PTR(skel, "skel_load"))
> +               goto cleanup;
> +
> +       attr.type = PERF_TYPE_BREAKPOINT;
> +       attr.size = sizeof(attr);
> +       attr.bp_type = HW_BREAKPOINT_X;
> +       attr.bp_addr = (uintptr_t)test_function;
> +       attr.bp_len = sizeof(long);
> +       attr.sample_period = 1;
> +       attr.sample_type = PERF_SAMPLE_IP;
> +       attr.pinned = 1;
> +       attr.exclude_kernel = 1;
> +       attr.exclude_hv = 1;
> +       attr.precise_ip = 3;
> +       attr.sigtrap = 1;
> +       attr.remove_on_exec = 1;
> +
> +       perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> +       if (perf_fd < 0 && (errno == ENOENT || errno == EOPNOTSUPP)) {
> +               printf("SKIP:no PERF_TYPE_BREAKPOINT/HW_BREAKPOINT_X\n");
> +               test__skip();
> +               goto cleanup;
> +       }
> +       if (!ASSERT_OK(perf_fd < 0, "perf_event_open"))
> +               goto cleanup;
> +
> +       /* Configure the perf event to signal on sample. */
> +       err = fcntl(perf_fd, F_SETFL, O_ASYNC);
> +       if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
> +               goto cleanup;
> +
> +       owner.type = F_OWNER_TID;
> +       owner.pid = syscall(__NR_gettid);
> +       err = fcntl(perf_fd, F_SETOWN_EX, &owner);
> +       if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> +               goto cleanup;
> +
> +       /*
> +        * Allow at most one sample. A sample rejected by bpf should
> +        * not count against this.
> +        */

Multi-line comment style should be like

        /* Allow at most one sample. A sample rejected by bpf should
        * not count against this.
        */

> +       err = ioctl(perf_fd, PERF_EVENT_IOC_REFRESH, 1);
> +       if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_REFRESH)"))
> +               goto cleanup;
> +
> +       prog_link = bpf_program__attach_perf_event(skel->progs.handler, perf_fd);
> +       if (!ASSERT_OK_PTR(prog_link, "bpf_program__attach_perf_event"))
> +               goto cleanup;
> +
> +       /* Configure the bpf program to suppress the sample. */
> +       skel->bss->ip = (uintptr_t)test_function;
> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 0, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 0, "sigtrap_count");
> +
> +       /* Configure the bpf program to allow the sample. */
> +       skel->bss->ip = 0;
> +       signals_unexpected = 0;
> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> +
> +       /*
> +        * Test that the sample above is the only one allowed (by perf, not
> +        * by bpf)
> +        */

ditto.

> +       test_function();
> +
> +       ASSERT_EQ(sigio_count, 1, "sigio_count");
> +       ASSERT_EQ(sigtrap_count, 1, "sigtrap_count");
> +
> +cleanup:
> +       bpf_link__destroy(prog_link);
> +       if (perf_fd >= 0)
> +               close(perf_fd);
> +       test_perf_skip__destroy(skel);
> +
> +       signal(SIGIO, previous_sigio);
> +       sigaction(SIGTRAP, &previous_sigtrap, NULL);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/test_perf_skip.c b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> new file mode 100644
> index 000000000000..7eb8b6de7a57
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> @@ -0,0 +1,15 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "vmlinux.h"
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +
> +uintptr_t ip;
> +
> +SEC("perf_event")
> +int handler(struct bpf_perf_event_data *data)
> +{
> +       /* Skip events that have the correct ip. */
> +       return ip != PT_REGS_IP(&data->regs);
> +}
> +
> +char _license[] SEC("license") = "GPL";
> --
> 2.34.1
>