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References: <20231204201406.341074-1-khuey@kylehuey.com> <20231204201406.341074-3-khuey@kylehuey.com>
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From:   Kyle Huey <me@kylehuey.com>
Date:   Tue, 5 Dec 2023 09:52:00 -0800
Message-ID: <CAP045Aos_o2Smeo_9C_LJNvCTKAF5Usatt0RAF-NeL0SjNJEYQ@mail.gmail.com>
Subject: Re: [PATCH 2/2] selftest/bpf: Test returning zero from a perf bpf
 program suppresses SIGIO.
To:     Yonghong Song <yonghong.song@linux.dev>
Cc:     Kyle Huey <khuey@kylehuey.com>, linux-kernel@vger.kernel.org,
        "Robert O'Callahan" <robert@ocallahan.org>,
        Andrii Nakryiko <andrii@kernel.org>,
        Mykola Lysenko <mykolal@fb.com>,
        Alexei Starovoitov <ast@kernel.org>,
        Daniel Borkmann <daniel@iogearbox.net>,
        Martin KaFai Lau <martin.lau@linux.dev>,
        Song Liu <song@kernel.org>,
        John Fastabend <john.fastabend@gmail.com>,
        KP Singh <kpsingh@kernel.org>,
        Stanislav Fomichev <sdf@google.com>,
        Hao Luo <haoluo@google.com>, Jiri Olsa <jolsa@kernel.org>,
        Shuah Khan <shuah@kernel.org>, bpf@vger.kernel.org,
        linux-kselftest@vger.kernel.org
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On Tue, Dec 5, 2023 at 8:54=E2=80=AFAM Yonghong Song <yonghong.song@linux.d=
ev> wrote:
>
>
> On 12/4/23 3:14 PM, Kyle Huey wrote:
> > The test sets a hardware breakpoint and uses a bpf program to suppress =
the
> > I/O availability signal if the ip matches the expected value.
> >
> > Signed-off-by: Kyle Huey <khuey@kylehuey.com>
> > ---
> >   .../selftests/bpf/prog_tests/perf_skip.c      | 95 ++++++++++++++++++=
+
> >   .../selftests/bpf/progs/test_perf_skip.c      | 23 +++++
> >   2 files changed, 118 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..b269a31669b7
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/prog_tests/perf_skip.c
> > @@ -0,0 +1,95 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#define _GNU_SOURCE
> > +#include <test_progs.h>
> > +#include "test_perf_skip.skel.h"
> > +#include <linux/hw_breakpoint.h>
> > +#include <sys/mman.h>
> > +
> > +#define BPF_OBJECT            "test_perf_skip.bpf.o"
> > +
> > +static void handle_sig(int)
>
> I hit a warning here:
> home/yhs/work/bpf-next/tools/testing/selftests/bpf/prog_tests/perf_skip.c=
:10:27: error: omitting the parameter name in a function definition is a C2=
3 extension [-Werror,-Wc23-extensions]

Yeah, Meta's kernel-ci bot sent me off-list email about this one.

>
>     10 | static void handle_sig(int)
>        |
>
> Add a parameter and marked as unused can resolve the issue.
>
> #define __always_unused         __attribute__((__unused__))
>
> static void handle_sig(int unused __always_unused)
> {
>          ASSERT_OK(1, "perf event not skipped");
> }
>
>
> > +{
> > +     ASSERT_OK(1, "perf event not skipped");
> > +}
> > +
> > +static noinline int test_function(void)
> > +{
> > +     return 0;
> > +}
> > +
> > +void serial_test_perf_skip(void)
> > +{
> > +     sighandler_t previous;
> > +     int duration =3D 0;
> > +     struct test_perf_skip *skel =3D NULL;
> > +     int map_fd =3D -1;
> > +     long page_size =3D sysconf(_SC_PAGE_SIZE);
> > +     uintptr_t *ip =3D NULL;
> > +     int prog_fd =3D -1;
> > +     struct perf_event_attr attr =3D {0};
> > +     int perf_fd =3D -1;
> > +     struct f_owner_ex owner;
> > +     int err;
> > +
> > +     previous =3D signal(SIGIO, handle_sig);
> > +
> > +     skel =3D test_perf_skip__open_and_load();
> > +     if (!ASSERT_OK_PTR(skel, "skel_load"))
> > +             goto cleanup;
> > +
> > +     prog_fd =3D bpf_program__fd(skel->progs.handler);
> > +     if (!ASSERT_OK(prog_fd < 0, "bpf_program__fd"))
> > +             goto cleanup;
> > +
> > +     map_fd =3D bpf_map__fd(skel->maps.ip);
> > +     if (!ASSERT_OK(map_fd < 0, "bpf_map__fd"))
> > +             goto cleanup;
> > +
> > +     ip =3D mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, =
map_fd, 0);
> > +     if (!ASSERT_OK_PTR(ip, "mmap bpf map"))
> > +             goto cleanup;
> > +
> > +     *ip =3D (uintptr_t)test_function;
> > +
> > +     attr.type =3D PERF_TYPE_BREAKPOINT;
> > +     attr.size =3D sizeof(attr);
> > +     attr.bp_type =3D HW_BREAKPOINT_X;
> > +     attr.bp_addr =3D (uintptr_t)test_function;
> > +     attr.bp_len =3D sizeof(long);
> > +     attr.sample_period =3D 1;
> > +     attr.sample_type =3D PERF_SAMPLE_IP;
> > +     attr.pinned =3D 1;
> > +     attr.exclude_kernel =3D 1;
> > +     attr.exclude_hv =3D 1;
> > +     attr.precise_ip =3D 3;
> > +
> > +     perf_fd =3D syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> > +     if (CHECK(perf_fd < 0, "perf_event_open", "err %d\n", perf_fd))
> > +             goto cleanup;
> > +
> > +     err =3D fcntl(perf_fd, F_SETFL, O_ASYNC);
> > +     if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
> > +             goto cleanup;
> > +
> > +     owner.type =3D F_OWNER_TID;
> > +     owner.pid =3D gettid();
>
> I hit a compilation failure here:
>
> /home/yhs/work/bpf-next/tools/testing/selftests/bpf/prog_tests/perf_skip.=
c:75:14: error: call to undeclared function 'gettid'; ISO C99 and later do =
not support implicit function declarations [-Wimplicit-function-declaration=
]
>     75 |         owner.pid =3D gettid();
>        |                     ^
>
> If you looked at some other examples, the common usage is do 'syscall(SYS=
_gettid)'.

Not clear why this works for me but sure I'll change that.

>
> So the following patch should fix the compilation error:
>
> #include <sys/syscall.h>
> ...
>          owner.pid =3D syscall(SYS_gettid);
> ...
>
> > +     err =3D fcntl(perf_fd, F_SETOWN_EX, &owner);
> > +     if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> > +             goto cleanup;
> > +
> > +     err =3D ioctl(perf_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
> > +     if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_SET_BPF)"))
> > +             goto cleanup;
> > +
> > +     test_function();
>
> As Andrii has mentioned in previous comments, we will have
> issue is RELEASE version of selftest is built
>    RELEASE=3D1 make ...
>
> See https://lore.kernel.org/bpf/20231127050342.1945270-1-yonghong.song@li=
nux.dev

Not sure I follow this one. Are you saying adding asm volatile ("") in
test_function() is *not* sufficient?

- Kyle

>
> > +
> > +cleanup:
> > +     if (perf_fd >=3D 0)
> > +             close(perf_fd);
> > +     if (ip)
> > +             munmap(ip, page_size);
> > +     if (skel)
> > +             test_perf_skip__destroy(skel);
> > +
> > +     signal(SIGIO, previous);
> > +}
> > 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..ef01a9161afe
> > --- /dev/null
> > +++ b/tools/testing/selftests/bpf/progs/test_perf_skip.c
> > @@ -0,0 +1,23 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +#include "vmlinux.h"
> > +#include <bpf/bpf_helpers.h>
> > +#include <bpf/bpf_tracing.h>
> > +
> > +struct {
> > +     __uint(type, BPF_MAP_TYPE_ARRAY);
> > +     __uint(max_entries, 1);
> > +     __uint(map_flags, BPF_F_MMAPABLE);
> > +     __type(key, uint32_t);
> > +     __type(value, uintptr_t);
> > +} ip SEC(".maps");
> > +
> > +SEC("perf_event")
> > +int handler(struct bpf_perf_event_data *data)
> > +{
> > +     const uint32_t index =3D 0;
> > +     uintptr_t *v =3D bpf_map_lookup_elem(&ip, &index);
> > +
> > +     return !(v && *v =3D=3D PT_REGS_IP(&data->regs));
> > +}
> > +
> > +char _license[] SEC("license") =3D "GPL";