lkml.org 
[lkml]   [2024]   [Jan]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH v3 4/4] selftest/bpf: Test a perf bpf program that suppresses side effects.
    On Tue, Jan 2, 2024 at 2:49 PM Song Liu <song@kernel.org> wrote:
    >
    > On Sun, Dec 10, 2023 at 8:56 PM Kyle Huey <me@kylehuey.com> 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@kylehuey.com>
    > > ---
    > > .../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;
    > }
    >

    I'll just drop signals_expected. Now that I'm counting the exact
    number of signals it's redundant.

    > > + ++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?

    Addressed in v4.

    > > +
    > > + 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

    Addressed in v4.

    > /* 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
    > >

    - Kyle

    \
     
     \ /
      Last update: 2024-01-19 01:12    [W:8.005 / U:0.028 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site