Merge branch 'bpf-perf-link'

Andrii Nakryiko says:

====================
This patch set implements an ability for users to specify custom black box u64
value for each BPF program attachment, bpf_cookie, which is available to BPF
program at runtime. This is a feature that's critically missing for cases when
some sort of generic processing needs to be done by the common BPF program
logic (or even exactly the same BPF program) across multiple BPF hooks (e.g.,
many uniformly handled kprobes) and it's important to be able to distinguish
between each BPF hook at runtime (e.g., for additional configuration lookup).

The choice of restricting this to a fixed-size 8-byte u64 value is an explicit
design decision. Making this configurable by users adds unnecessary complexity
(extra memory allocations, extra complications on the verifier side to validate
accesses to variable-sized data area) while not really opening up new
possibilities. If user's use case requires storing more data per attachment,
it's possible to use either global array, or ARRAY/HASHMAP BPF maps, where
bpf_cookie would be used as an index into respective storage, populated by
user-space code before creating BPF link. This gives user all the flexibility
and control while keeping BPF verifier and BPF helper API simple.

Currently, similar functionality can only be achieved through:

  - code-generation and BPF program cloning, which is very complicated and
    unmaintainable;
  - on-the-fly C code generation and further runtime compilation, which is
    what BCC uses and allows to do pretty simply. The big downside is a very
    heavy-weight Clang/LLVM dependency and inefficient memory usage (due to
    many BPF program clones and the compilation process itself);
  - in some cases (kprobes and sometimes uprobes) it's possible to do function
    IP lookup to get function-specific configuration. This doesn't work for
    all the cases (e.g., when attaching uprobes to shared libraries) and has
    higher runtime overhead and additional programming complexity due to
    BPF_MAP_TYPE_HASHMAP lookups. Up until recently, before bpf_get_func_ip()
    BPF helper was added, it was also very complicated and unstable (API-wise)
    to get traced function's IP from fentry/fexit and kretprobe.

With libbpf and BPF CO-RE, runtime compilation is not an option, so to be able
to build generic tracing tooling simply and efficiently, ability to provide
additional bpf_cookie value for each *attachment* (as opposed to each BPF
program) is extremely important. Two immediate users of this functionality are
going to be libbpf-based USDT library (currently in development) and retsnoop
([0]), but I'm sure more applications will come once users get this feature in
their kernels.

To achieve above described, all perf_event-based BPF hooks are made available
through a new BPF_LINK_TYPE_PERF_EVENT BPF link, which allows to use common
LINK_CREATE command for program attachments and generally brings
perf_event-based attachments into a common BPF link infrastructure.

With that, LINK_CREATE gets ability to pass throught bpf_cookie value during
link creation (BPF program attachment) time. bpf_get_attach_cookie() BPF
helper is added to allow fetching this value at runtime from BPF program side.
BPF cookie is stored either on struct perf_event itself and fetched from the
BPF program context, or is passed through ambient BPF run context, added in
c7603cfa04e7 ("bpf: Add ambient BPF runtime context stored in current").

On the libbpf side of things, BPF perf link is utilized whenever is supported
by the kernel instead of using PERF_EVENT_IOC_SET_BPF ioctl on perf_event FD.
All the tracing attach APIs are extended with OPTS and bpf_cookie is passed
through corresponding opts structs.

Last part of the patch set adds few self-tests utilizing new APIs.

There are also a few refactorings along the way to make things cleaner and
easier to work with, both in kernel (BPF_PROG_RUN and BPF_PROG_RUN_ARRAY), and
throughout libbpf and selftests.

Follow-up patches will extend bpf_cookie to fentry/fexit programs.

While adding uprobe_opts, also extend it with ref_ctr_offset for specifying
USDT semaphore (reference counter) offset. Update attach_probe selftests to
validate its functionality. This is another feature (along with bpf_cookie)
required for implementing libbpf-based USDT solution.

  [0] https://github.com/anakryiko/retsnoop

v4->v5:
  - rebase on latest bpf-next to resolve merge conflict;
  - add ref_ctr_offset to uprobe_opts and corresponding selftest;
v3->v4:
  - get rid of BPF_PROG_RUN macro in favor of bpf_prog_run() (Daniel);
  - move #ifdef CONFIG_BPF_SYSCALL check into bpf_set_run_ctx (Daniel);
v2->v3:
  - user_ctx -> bpf_cookie, bpf_get_user_ctx -> bpf_get_attach_cookie (Peter);
  - fix BPF_LINK_TYPE_PERF_EVENT value fix (Jiri);
  - use bpf_prog_run() from bpf_prog_run_pin_on_cpu() (Yonghong);
v1->v2:
  - fix build failures on non-x86 arches by gating on CONFIG_PERF_EVENTS.
====================

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

3 files changed, 371 insertions, 70 deletions

diff --git a/tools/testing/selftests/bpf/prog_tests/attach_probe.c b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
index ec11e20d2b92..bf307bb9e446 100644
--- a/tools/testing/selftests/bpf/prog_tests/attach_probe.c
+++ b/tools/testing/selftests/bpf/prog_tests/attach_probe.c
@@ -2,79 +2,28 @@
 #include <test_progs.h>
 #include "test_attach_probe.skel.h"
 
-#if defined(__powerpc64__) && defined(_CALL_ELF) && _CALL_ELF == 2
-
-#define OP_RT_RA_MASK   0xffff0000UL
-#define LIS_R2          0x3c400000UL
-#define ADDIS_R2_R12    0x3c4c0000UL
-#define ADDI_R2_R2      0x38420000UL
-
-static ssize_t get_offset(ssize_t addr, ssize_t base)
-{
-	u32 *insn = (u32 *) addr;
-
-	/*
-	 * A PPC64 ABIv2 function may have a local and a global entry
-	 * point. We need to use the local entry point when patching
-	 * functions, so identify and step over the global entry point
-	 * sequence.
-	 *
-	 * The global entry point sequence is always of the form:
-	 *
-	 * addis r2,r12,XXXX
-	 * addi  r2,r2,XXXX
-	 *
-	 * A linker optimisation may convert the addis to lis:
-	 *
-	 * lis   r2,XXXX
-	 * addi  r2,r2,XXXX
-	 */
-	if ((((*insn & OP_RT_RA_MASK) == ADDIS_R2_R12) ||
-	     ((*insn & OP_RT_RA_MASK) == LIS_R2)) &&
-	    ((*(insn + 1) & OP_RT_RA_MASK) == ADDI_R2_R2))
-		return (ssize_t)(insn + 2) - base;
-	else
-		return addr - base;
-}
-#else
-#define get_offset(addr, base) (addr - base)
-#endif
-
-ssize_t get_base_addr() {
-	size_t start, offset;
-	char buf[256];
-	FILE *f;
-
-	f = fopen("/proc/self/maps", "r");
-	if (!f)
-		return -errno;
-
-	while (fscanf(f, "%zx-%*x %s %zx %*[^\n]\n",
-		      &start, buf, &offset) == 3) {
-		if (strcmp(buf, "r-xp") == 0) {
-			fclose(f);
-			return start - offset;
-		}
-	}
-
-	fclose(f);
-	return -EINVAL;
-}
+/* this is how USDT semaphore is actually defined, except volatile modifier */
+volatile unsigned short uprobe_ref_ctr __attribute__((unused)) __attribute((section(".probes")));
 
 void test_attach_probe(void)
 {
+	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, uprobe_opts);
 	int duration = 0;
 	struct bpf_link *kprobe_link, *kretprobe_link;
 	struct bpf_link *uprobe_link, *uretprobe_link;
 	struct test_attach_probe* skel;
 	size_t uprobe_offset;
-	ssize_t base_addr;
+	ssize_t base_addr, ref_ctr_offset;
 
 	base_addr = get_base_addr();
 	if (CHECK(base_addr < 0, "get_base_addr",
 		  "failed to find base addr: %zd", base_addr))
 		return;
-	uprobe_offset = get_offset((size_t)&get_base_addr, base_addr);
+	uprobe_offset = get_uprobe_offset(&get_base_addr, base_addr);
+
+	ref_ctr_offset = get_rel_offset((uintptr_t)&uprobe_ref_ctr);
+	if (!ASSERT_GE(ref_ctr_offset, 0, "ref_ctr_offset"))
+		return;
 
 	skel = test_attach_probe__open_and_load();
 	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
@@ -96,20 +45,28 @@ void test_attach_probe(void)
 		goto cleanup;
 	skel->links.handle_kretprobe = kretprobe_link;
 
-	uprobe_link = bpf_program__attach_uprobe(skel->progs.handle_uprobe,
-						 false /* retprobe */,
-						 0 /* self pid */,
-						 "/proc/self/exe",
-						 uprobe_offset);
+	ASSERT_EQ(uprobe_ref_ctr, 0, "uprobe_ref_ctr_before");
+
+	uprobe_opts.retprobe = false;
+	uprobe_opts.ref_ctr_offset = ref_ctr_offset;
+	uprobe_link = bpf_program__attach_uprobe_opts(skel->progs.handle_uprobe,
+						      0 /* self pid */,
+						      "/proc/self/exe",
+						      uprobe_offset,
+						      &uprobe_opts);
 	if (!ASSERT_OK_PTR(uprobe_link, "attach_uprobe"))
 		goto cleanup;
 	skel->links.handle_uprobe = uprobe_link;
 
-	uretprobe_link = bpf_program__attach_uprobe(skel->progs.handle_uretprobe,
-						    true /* retprobe */,
-						    -1 /* any pid */,
-						    "/proc/self/exe",
-						    uprobe_offset);
+	ASSERT_GT(uprobe_ref_ctr, 0, "uprobe_ref_ctr_after");
+
+	/* if uprobe uses ref_ctr, uretprobe has to use ref_ctr as well */
+	uprobe_opts.retprobe = true;
+	uprobe_opts.ref_ctr_offset = ref_ctr_offset;
+	uretprobe_link = bpf_program__attach_uprobe_opts(skel->progs.handle_uretprobe,
+							 -1 /* any pid */,
+							 "/proc/self/exe",
+							 uprobe_offset, &uprobe_opts);
 	if (!ASSERT_OK_PTR(uretprobe_link, "attach_uretprobe"))
 		goto cleanup;
 	skel->links.handle_uretprobe = uretprobe_link;
@@ -136,4 +93,5 @@ void test_attach_probe(void)
 
 cleanup:
 	test_attach_probe__destroy(skel);
+	ASSERT_EQ(uprobe_ref_ctr, 0, "uprobe_ref_ctr_cleanup");
 }
diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
new file mode 100644
index 000000000000..5eea3c3a40fe
--- /dev/null
+++ b/tools/testing/selftests/bpf/prog_tests/bpf_cookie.c
@@ -0,0 +1,254 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Copyright (c) 2021 Facebook */
+#define _GNU_SOURCE
+#include <pthread.h>
+#include <sched.h>
+#include <sys/syscall.h>
+#include <unistd.h>
+#include <test_progs.h>
+#include "test_bpf_cookie.skel.h"
+
+static void kprobe_subtest(struct test_bpf_cookie *skel)
+{
+	DECLARE_LIBBPF_OPTS(bpf_kprobe_opts, opts);
+	struct bpf_link *link1 = NULL, *link2 = NULL;
+	struct bpf_link *retlink1 = NULL, *retlink2 = NULL;
+
+	/* attach two kprobes */
+	opts.bpf_cookie = 0x1;
+	opts.retprobe = false;
+	link1 = bpf_program__attach_kprobe_opts(skel->progs.handle_kprobe,
+						 SYS_NANOSLEEP_KPROBE_NAME, &opts);
+	if (!ASSERT_OK_PTR(link1, "link1"))
+		goto cleanup;
+
+	opts.bpf_cookie = 0x2;
+	opts.retprobe = false;
+	link2 = bpf_program__attach_kprobe_opts(skel->progs.handle_kprobe,
+						 SYS_NANOSLEEP_KPROBE_NAME, &opts);
+	if (!ASSERT_OK_PTR(link2, "link2"))
+		goto cleanup;
+
+	/* attach two kretprobes */
+	opts.bpf_cookie = 0x10;
+	opts.retprobe = true;
+	retlink1 = bpf_program__attach_kprobe_opts(skel->progs.handle_kretprobe,
+						    SYS_NANOSLEEP_KPROBE_NAME, &opts);
+	if (!ASSERT_OK_PTR(retlink1, "retlink1"))
+		goto cleanup;
+
+	opts.bpf_cookie = 0x20;
+	opts.retprobe = true;
+	retlink2 = bpf_program__attach_kprobe_opts(skel->progs.handle_kretprobe,
+						    SYS_NANOSLEEP_KPROBE_NAME, &opts);
+	if (!ASSERT_OK_PTR(retlink2, "retlink2"))
+		goto cleanup;
+
+	/* trigger kprobe && kretprobe */
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->kprobe_res, 0x1 | 0x2, "kprobe_res");
+	ASSERT_EQ(skel->bss->kretprobe_res, 0x10 | 0x20, "kretprobe_res");
+
+cleanup:
+	bpf_link__destroy(link1);
+	bpf_link__destroy(link2);
+	bpf_link__destroy(retlink1);
+	bpf_link__destroy(retlink2);
+}
+
+static void uprobe_subtest(struct test_bpf_cookie *skel)
+{
+	DECLARE_LIBBPF_OPTS(bpf_uprobe_opts, opts);
+	struct bpf_link *link1 = NULL, *link2 = NULL;
+	struct bpf_link *retlink1 = NULL, *retlink2 = NULL;
+	size_t uprobe_offset;
+	ssize_t base_addr;
+
+	base_addr = get_base_addr();
+	uprobe_offset = get_uprobe_offset(&get_base_addr, base_addr);
+
+	/* attach two uprobes */
+	opts.bpf_cookie = 0x100;
+	opts.retprobe = false;
+	link1 = bpf_program__attach_uprobe_opts(skel->progs.handle_uprobe, 0 /* self pid */,
+						"/proc/self/exe", uprobe_offset, &opts);
+	if (!ASSERT_OK_PTR(link1, "link1"))
+		goto cleanup;
+
+	opts.bpf_cookie = 0x200;
+	opts.retprobe = false;
+	link2 = bpf_program__attach_uprobe_opts(skel->progs.handle_uprobe, -1 /* any pid */,
+						"/proc/self/exe", uprobe_offset, &opts);
+	if (!ASSERT_OK_PTR(link2, "link2"))
+		goto cleanup;
+
+	/* attach two uretprobes */
+	opts.bpf_cookie = 0x1000;
+	opts.retprobe = true;
+	retlink1 = bpf_program__attach_uprobe_opts(skel->progs.handle_uretprobe, -1 /* any pid */,
+						   "/proc/self/exe", uprobe_offset, &opts);
+	if (!ASSERT_OK_PTR(retlink1, "retlink1"))
+		goto cleanup;
+
+	opts.bpf_cookie = 0x2000;
+	opts.retprobe = true;
+	retlink2 = bpf_program__attach_uprobe_opts(skel->progs.handle_uretprobe, 0 /* self pid */,
+						   "/proc/self/exe", uprobe_offset, &opts);
+	if (!ASSERT_OK_PTR(retlink2, "retlink2"))
+		goto cleanup;
+
+	/* trigger uprobe && uretprobe */
+	get_base_addr();
+
+	ASSERT_EQ(skel->bss->uprobe_res, 0x100 | 0x200, "uprobe_res");
+	ASSERT_EQ(skel->bss->uretprobe_res, 0x1000 | 0x2000, "uretprobe_res");
+
+cleanup:
+	bpf_link__destroy(link1);
+	bpf_link__destroy(link2);
+	bpf_link__destroy(retlink1);
+	bpf_link__destroy(retlink2);
+}
+
+static void tp_subtest(struct test_bpf_cookie *skel)
+{
+	DECLARE_LIBBPF_OPTS(bpf_tracepoint_opts, opts);
+	struct bpf_link *link1 = NULL, *link2 = NULL, *link3 = NULL;
+
+	/* attach first tp prog */
+	opts.bpf_cookie = 0x10000;
+	link1 = bpf_program__attach_tracepoint_opts(skel->progs.handle_tp1,
+						    "syscalls", "sys_enter_nanosleep", &opts);
+	if (!ASSERT_OK_PTR(link1, "link1"))
+		goto cleanup;
+
+	/* attach second tp prog */
+	opts.bpf_cookie = 0x20000;
+	link2 = bpf_program__attach_tracepoint_opts(skel->progs.handle_tp2,
+						    "syscalls", "sys_enter_nanosleep", &opts);
+	if (!ASSERT_OK_PTR(link2, "link2"))
+		goto cleanup;
+
+	/* trigger tracepoints */
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->tp_res, 0x10000 | 0x20000, "tp_res1");
+
+	/* now we detach first prog and will attach third one, which causes
+	 * two internal calls to bpf_prog_array_copy(), shuffling
+	 * bpf_prog_array_items around. We test here that we don't lose track
+	 * of associated bpf_cookies.
+	 */
+	bpf_link__destroy(link1);
+	link1 = NULL;
+	kern_sync_rcu();
+	skel->bss->tp_res = 0;
+
+	/* attach third tp prog */
+	opts.bpf_cookie = 0x40000;
+	link3 = bpf_program__attach_tracepoint_opts(skel->progs.handle_tp3,
+						    "syscalls", "sys_enter_nanosleep", &opts);
+	if (!ASSERT_OK_PTR(link3, "link3"))
+		goto cleanup;
+
+	/* trigger tracepoints */
+	usleep(1);
+
+	ASSERT_EQ(skel->bss->tp_res, 0x20000 | 0x40000, "tp_res2");
+
+cleanup:
+	bpf_link__destroy(link1);
+	bpf_link__destroy(link2);
+	bpf_link__destroy(link3);
+}
+
+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;
+}
+
+static void pe_subtest(struct test_bpf_cookie *skel)
+{
+	DECLARE_LIBBPF_OPTS(bpf_perf_event_opts, opts);
+	struct bpf_link *link = NULL;
+	struct perf_event_attr attr;
+	int pfd = -1;
+
+	/* 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;
+
+	opts.bpf_cookie = 0x100000;
+	link = bpf_program__attach_perf_event_opts(skel->progs.handle_pe, pfd, &opts);
+	if (!ASSERT_OK_PTR(link, "link1"))
+		goto cleanup;
+
+	burn_cpu(); /* trigger BPF prog */
+
+	ASSERT_EQ(skel->bss->pe_res, 0x100000, "pe_res1");
+
+	/* prevent bpf_link__destroy() closing pfd itself */
+	bpf_link__disconnect(link);
+	/* close BPF link's FD explicitly */
+	close(bpf_link__fd(link));
+	/* free up memory used by struct bpf_link */
+	bpf_link__destroy(link);
+	link = NULL;
+	kern_sync_rcu();
+	skel->bss->pe_res = 0;
+
+	opts.bpf_cookie = 0x200000;
+	link = bpf_program__attach_perf_event_opts(skel->progs.handle_pe, pfd, &opts);
+	if (!ASSERT_OK_PTR(link, "link2"))
+		goto cleanup;
+
+	burn_cpu(); /* trigger BPF prog */
+
+	ASSERT_EQ(skel->bss->pe_res, 0x200000, "pe_res2");
+
+cleanup:
+	close(pfd);
+	bpf_link__destroy(link);
+}
+
+void test_bpf_cookie(void)
+{
+	struct test_bpf_cookie *skel;
+
+	skel = test_bpf_cookie__open_and_load();
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
+		return;
+
+	skel->bss->my_tid = syscall(SYS_gettid);
+
+	if (test__start_subtest("kprobe"))
+		kprobe_subtest(skel);
+	if (test__start_subtest("uprobe"))
+		uprobe_subtest(skel);
+	if (test__start_subtest("tracepoint"))
+		tp_subtest(skel);
+	if (test__start_subtest("perf_event"))
+		pe_subtest(skel);
+
+	test_bpf_cookie__destroy(skel);
+}
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
index 000000000000..b1abd0c46607
--- /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);
+}