Re: [PATCH 2/2] selftest/bpf: Test returning zero from a perf bpf program suppresses SIGIO.

From: Kyle Huey <me@kylehuey.com>
To: Andrii Nakryiko <andrii.nakryiko@gmail.com>
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>,
	Yonghong Song <yonghong.song@linux.dev>,
	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
Subject: Re: [PATCH 2/2] selftest/bpf: Test returning zero from a perf bpf program suppresses SIGIO.
Date: Tue, 5 Dec 2023 10:21:25 -0800	[thread overview]
Message-ID: <CAP045ArrF81xNqRZcW=8Uw7R2Vvgman1QODbt7wgL_U6HKQ6Mg@mail.gmail.com> (raw)
In-Reply-To: <CAEf4BzbDKiP7femK5DZ8jeyK0u63KrV+FogEDVPaYS7mc4if7g@mail.gmail.com>

On Mon, Dec 4, 2023 at 2:14 PM Andrii Nakryiko
<andrii.nakryiko@gmail.com> wrote:
>
> On Mon, Dec 4, 2023 at 12:14 PM Kyle Huey <me@kylehuey.com> 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"
>
> leftover?

Indeed. Fixed.

> > +
> > +static void handle_sig(int)
> > +{
> > +       ASSERT_OK(1, "perf event not skipped");
> > +}
> > +
> > +static noinline int test_function(void)
> > +{
>
> please add
>
> asm volatile ("");
>
> here to prevent compiler from actually inlining at the call site

Ok.

> > +       return 0;
> > +}
> > +
> > +void serial_test_perf_skip(void)
> > +{
> > +       sighandler_t previous;
> > +       int duration = 0;
> > +       struct test_perf_skip *skel = NULL;
> > +       int map_fd = -1;
> > +       long page_size = sysconf(_SC_PAGE_SIZE);
> > +       uintptr_t *ip = NULL;
> > +       int prog_fd = -1;
> > +       struct perf_event_attr attr = {0};
> > +       int perf_fd = -1;
> > +       struct f_owner_ex owner;
> > +       int err;
> > +
> > +       previous = signal(SIGIO, handle_sig);
> > +
> > +       skel = test_perf_skip__open_and_load();
> > +       if (!ASSERT_OK_PTR(skel, "skel_load"))
> > +               goto cleanup;
> > +
> > +       prog_fd = bpf_program__fd(skel->progs.handler);
> > +       if (!ASSERT_OK(prog_fd < 0, "bpf_program__fd"))
> > +               goto cleanup;
> > +
> > +       map_fd = bpf_map__fd(skel->maps.ip);
> > +       if (!ASSERT_OK(map_fd < 0, "bpf_map__fd"))
> > +               goto cleanup;
> > +
> > +       ip = mmap(NULL, page_size, PROT_READ | PROT_WRITE, MAP_SHARED, map_fd, 0);
> > +       if (!ASSERT_OK_PTR(ip, "mmap bpf map"))
> > +               goto cleanup;
> > +
> > +       *ip = (uintptr_t)test_function;
> > +
> > +       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;
> > +
> > +       perf_fd = syscall(__NR_perf_event_open, &attr, 0, -1, -1, 0);
> > +       if (CHECK(perf_fd < 0, "perf_event_open", "err %d\n", perf_fd))
>
> please don't use CHECK() macro, stick to ASSERT_xxx()

Done.

> also, we are going to run all this on different hardware and VMs, see
> how we skip tests if hardware support is not there. See test__skip
> usage in prog_tests/perf_branches.c, as one example

Hmm I suppose it should be conditioned on CONFIG_HAVE_HW_BREAKPOINT.

> > +               goto cleanup;
> > +
> > +       err = fcntl(perf_fd, F_SETFL, O_ASYNC);
>
> I assume this is what will send SIGIO, right? Can you add a small
> comment explicitly saying this?

Done.

> > +       if (!ASSERT_OK(err, "fcntl(F_SETFL, O_ASYNC)"))
> > +               goto cleanup;
> > +
> > +       owner.type = F_OWNER_TID;
> > +       owner.pid = gettid();
> > +       err = fcntl(perf_fd, F_SETOWN_EX, &owner);
> > +       if (!ASSERT_OK(err, "fcntl(F_SETOWN_EX)"))
> > +               goto cleanup;
> > +
> > +       err = ioctl(perf_fd, PERF_EVENT_IOC_SET_BPF, prog_fd);
> > +       if (!ASSERT_OK(err, "ioctl(PERF_EVENT_IOC_SET_BPF)"))
> > +               goto cleanup;
>
> we have a better way to do this, please use
> bpf_program__attach_perf_event() instead

Done.

> > +
> > +       test_function();
> > +
> > +cleanup:
> > +       if (perf_fd >= 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");
>
> please use global variable:
>
> __u64 ip;
>
> and then access it from user-space side through skeleton
>
> skel->bss.ip = &test_function;

Done.

> > +
> > +SEC("perf_event")
> > +int handler(struct bpf_perf_event_data *data)
> > +{
> > +       const uint32_t index = 0;
> > +       uintptr_t *v = bpf_map_lookup_elem(&ip, &index);
> > +
> > +       return !(v && *v == PT_REGS_IP(&data->regs));
>
> and so we the above global var suggestion this will be just:
>
> return ip == PT_REGS_IP(&data->regs);
>
> > +}
> > +
> > +char _license[] SEC("license") = "GPL";
> > --
> > 2.34.1
> >

- Kyle