selftests/bpf: Test low-level perf BPF link API

Add tests utilizing low-level bpf_link_create() API to create perf BPF link.

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210815070609.987780-13-andrii@kernel.org

diff --git a/tools/testing/selftests/bpf/prog_tests/perf_link.c b/tools/testing/selftests/bpf/prog_tests/perf_link.c
new file mode 100644 (file)
index 0000000..b1abd0c
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/perf_link.c
@@ -0,0 +1,89 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#define _GNU_SOURCE
+#include <pthread.h>
+#include <sched.h>
+#include <test_progs.h>
+#include "test_perf_link.skel.h"
+
+static void burn_cpu(void)
+{
+       volatile int j = 0;
+       cpu_set_t cpu_set;
+       int i, err;
+
+       /* generate some branches on cpu 0 */
+       CPU_ZERO(&cpu_set);
+       CPU_SET(0, &cpu_set);
+       err = pthread_setaffinity_np(pthread_self(), sizeof(cpu_set), &cpu_set);
+       ASSERT_OK(err, "set_thread_affinity");
+
+       /* spin the loop for a while (random high number) */
+       for (i = 0; i < 1000000; ++i)
+               ++j;
+}
+
+void test_perf_link(void)
+{
+       struct test_perf_link *skel = NULL;
+       struct perf_event_attr attr;
+       int pfd = -1, link_fd = -1, err;
+       int run_cnt_before, run_cnt_after;
+       struct bpf_link_info info;
+       __u32 info_len = sizeof(info);
+
+       /* create perf event */
+       memset(&attr, 0, sizeof(attr));
+       attr.size = sizeof(attr);
+       attr.type = PERF_TYPE_SOFTWARE;
+       attr.config = PERF_COUNT_SW_CPU_CLOCK;
+       attr.freq = 1;
+       attr.sample_freq = 4000;
+       pfd = syscall(__NR_perf_event_open, &attr, -1, 0, -1, PERF_FLAG_FD_CLOEXEC);
+       if (!ASSERT_GE(pfd, 0, "perf_fd"))
+               goto cleanup;
+
+       skel = test_perf_link__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "skel_load"))
+               goto cleanup;
+
+       link_fd = bpf_link_create(bpf_program__fd(skel->progs.handler), pfd,
+                                 BPF_PERF_EVENT, NULL);
+       if (!ASSERT_GE(link_fd, 0, "link_fd"))
+               goto cleanup;
+
+       memset(&info, 0, sizeof(info));
+       err = bpf_obj_get_info_by_fd(link_fd, &info, &info_len);
+       if (!ASSERT_OK(err, "link_get_info"))
+               goto cleanup;
+
+       ASSERT_EQ(info.type, BPF_LINK_TYPE_PERF_EVENT, "link_type");
+       ASSERT_GT(info.id, 0, "link_id");
+       ASSERT_GT(info.prog_id, 0, "link_prog_id");
+
+       /* ensure we get at least one perf_event prog execution */
+       burn_cpu();
+       ASSERT_GT(skel->bss->run_cnt, 0, "run_cnt");
+
+       /* perf_event is still active, but we close link and BPF program
+        * shouldn't be executed anymore
+        */
+       close(link_fd);
+       link_fd = -1;
+
+       /* make sure there are no stragglers */
+       kern_sync_rcu();
+
+       run_cnt_before = skel->bss->run_cnt;
+       burn_cpu();
+       run_cnt_after = skel->bss->run_cnt;
+
+       ASSERT_EQ(run_cnt_before, run_cnt_after, "run_cnt_before_after");
+
+cleanup:
+       if (link_fd >= 0)
+               close(link_fd);
+       if (pfd >= 0)
+               close(pfd);
+       test_perf_link__destroy(skel);
+}

diff --git a/tools/testing/selftests/bpf/progs/test_perf_link.c b/tools/testing/selftests/bpf/progs/test_perf_link.c
new file mode 100644 (file)
index 0000000..c1db9fd
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/test_perf_link.c
@@ -0,0 +1,16 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#include "vmlinux.h"
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+int run_cnt = 0;
+
+SEC("perf_event")
+int handler(struct pt_regs *ctx)
+{
+       __sync_fetch_and_add(&run_cnt, 1);
+       return 0;
+}
+
+char _license[] SEC("license") = "GPL";