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Date: Thu, 10 Mar 2022 15:21:17 -0800
From: Yonghong Song <yhs@...com>
To: Namhyung Kim <namhyung@...nel.org>,
Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>,
Andrii Nakryiko <andrii@...nel.org>
Cc: Martin KaFai Lau <kafai@...com>, Song Liu <songliubraving@...com>,
John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, netdev@...r.kernel.org,
bpf@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Eugene Loh <eugene.loh@...cle.com>, Hao Luo <haoluo@...gle.com>
Subject: Re: [PATCH 2/2] bpf/selftests: Test skipping stacktrace
On 3/10/22 12:22 AM, Namhyung Kim wrote:
> Add a test case for stacktrace with skip > 0 using a small sized
> buffer. It didn't support skipping entries greater than or equal to
> the size of buffer and filled the skipped part with 0.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> .../bpf/prog_tests/stacktrace_map_skip.c | 72 ++++++++++++++++
> .../selftests/bpf/progs/stacktrace_map_skip.c | 82 +++++++++++++++++++
> 2 files changed, 154 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/prog_tests/stacktrace_map_skip.c
> create mode 100644 tools/testing/selftests/bpf/progs/stacktrace_map_skip.c
>
> diff --git a/tools/testing/selftests/bpf/prog_tests/stacktrace_map_skip.c b/tools/testing/selftests/bpf/prog_tests/stacktrace_map_skip.c
> new file mode 100644
> index 000000000000..bcb244aa3c78
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/stacktrace_map_skip.c
> @@ -0,0 +1,72 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <test_progs.h>
> +#include "stacktrace_map_skip.skel.h"
> +
> +#define TEST_STACK_DEPTH 2
> +
> +void test_stacktrace_map_skip(void)
> +{
> + struct stacktrace_map_skip *skel;
> + int control_map_fd, stackid_hmap_fd, stackmap_fd, stack_amap_fd;
> + int err, stack_trace_len;
> + __u32 key, val, duration = 0;
> +
> + skel = stacktrace_map_skip__open_and_load();
> + if (CHECK(!skel, "skel_open_and_load", "skeleton open failed\n"))
> + return;
Please use ASSERT_* macros instead of CHECK* macros.
You can see other prog_tests/*.c files for examples.
> +
> + /* find map fds */
> + control_map_fd = bpf_map__fd(skel->maps.control_map);
> + if (CHECK_FAIL(control_map_fd < 0))
> + goto out;
> +
> + stackid_hmap_fd = bpf_map__fd(skel->maps.stackid_hmap);
> + if (CHECK_FAIL(stackid_hmap_fd < 0))
> + goto out;
> +
> + stackmap_fd = bpf_map__fd(skel->maps.stackmap);
> + if (CHECK_FAIL(stackmap_fd < 0))
> + goto out;
> +
> + stack_amap_fd = bpf_map__fd(skel->maps.stack_amap);
> + if (CHECK_FAIL(stack_amap_fd < 0))
> + goto out;
> +
> + err = stacktrace_map_skip__attach(skel);
> + if (CHECK(err, "skel_attach", "skeleton attach failed\n"))
> + goto out;
> +
> + /* give some time for bpf program run */
> + sleep(1);
> +
> + /* disable stack trace collection */
> + key = 0;
> + val = 1;
> + bpf_map_update_elem(control_map_fd, &key, &val, 0);
> +
> + /* for every element in stackid_hmap, we can find a corresponding one
> + * in stackmap, and vise versa.
> + */
> + err = compare_map_keys(stackid_hmap_fd, stackmap_fd);
> + if (CHECK(err, "compare_map_keys stackid_hmap vs. stackmap",
> + "err %d errno %d\n", err, errno))
> + goto out;
> +
> + err = compare_map_keys(stackmap_fd, stackid_hmap_fd);
> + if (CHECK(err, "compare_map_keys stackmap vs. stackid_hmap",
> + "err %d errno %d\n", err, errno))
> + goto out;
> +
> + stack_trace_len = TEST_STACK_DEPTH * sizeof(__u64);
> + err = compare_stack_ips(stackmap_fd, stack_amap_fd, stack_trace_len);
> + if (CHECK(err, "compare_stack_ips stackmap vs. stack_amap",
> + "err %d errno %d\n", err, errno))
> + goto out;
> +
> + if (CHECK(skel->bss->failed, "check skip",
> + "failed to skip some depth: %d", skel->bss->failed))
> + goto out;
> +
> +out:
> + stacktrace_map_skip__destroy(skel);
> +}
> diff --git a/tools/testing/selftests/bpf/progs/stacktrace_map_skip.c b/tools/testing/selftests/bpf/progs/stacktrace_map_skip.c
> new file mode 100644
> index 000000000000..323248b17ae4
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/stacktrace_map_skip.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <vmlinux.h>
> +#include <bpf/bpf_helpers.h>
> +
> +#define TEST_STACK_DEPTH 2
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_ARRAY);
> + __uint(max_entries, 1);
> + __type(key, __u32);
> + __type(value, __u32);
> +} control_map SEC(".maps");
You can use a global variable for this.
The global variable can be assigned a value (if needed, e.g., non-zero)
before skeleton open and load.
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_HASH);
> + __uint(max_entries, 16384);
> + __type(key, __u32);
> + __type(value, __u32);
> +} stackid_hmap SEC(".maps");
> +
> +typedef __u64 stack_trace_t[TEST_STACK_DEPTH];
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_STACK_TRACE);
> + __uint(max_entries, 16384);
> + __type(key, __u32);
> + __type(value, stack_trace_t);
> +} stackmap SEC(".maps");
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_ARRAY);
> + __uint(max_entries, 16384);
> + __type(key, __u32);
> + __type(value, stack_trace_t);
> +} stack_amap SEC(".maps");
> +
> +/* taken from /sys/kernel/debug/tracing/events/sched/sched_switch/format */
> +struct sched_switch_args {
> + unsigned long long pad;
> + char prev_comm[TASK_COMM_LEN];
> + int prev_pid;
> + int prev_prio;
> + long long prev_state;
> + char next_comm[TASK_COMM_LEN];
> + int next_pid;
> + int next_prio;
> +};
You can use this structure in vmlinux.h instead of the above:
struct trace_event_raw_sched_switch {
struct trace_entry ent;
char prev_comm[16];
pid_t prev_pid;
int prev_prio;
long int prev_state;
char next_comm[16];
pid_t next_pid;
int next_prio;
char __data[0];
};
> +
> +int failed = 0;
> +
> +SEC("tracepoint/sched/sched_switch")
> +int oncpu(struct sched_switch_args *ctx)
> +{
> + __u32 max_len = TEST_STACK_DEPTH * sizeof(__u64);
> + __u32 key = 0, val = 0, *value_p;
> + __u64 *stack_p;
> +
> + value_p = bpf_map_lookup_elem(&control_map, &key);
> + if (value_p && *value_p)
> + return 0; /* skip if non-zero *value_p */
> +
> + /* it should allow skipping whole buffer size entries */
> + key = bpf_get_stackid(ctx, &stackmap, TEST_STACK_DEPTH);
> + if ((int)key >= 0) {
> + /* The size of stackmap and stack_amap should be the same */
> + bpf_map_update_elem(&stackid_hmap, &key, &val, 0);
> + stack_p = bpf_map_lookup_elem(&stack_amap, &key);
> + if (stack_p) {
> + bpf_get_stack(ctx, stack_p, max_len, TEST_STACK_DEPTH);
> + /* it wrongly skipped all the entries and filled zero */
> + if (stack_p[0] == 0)
> + failed = 1;
> + }
> + } else if ((int)key == -14/*EFAULT*/) {
> + /* old kernel doesn't support skipping that many entries */
> + failed = 2;
The selftest is supposed to run with the kernel in the same code base.
So it is okay to skip the above 'if' test and just set failed = 2.
> + }
> +
> + return 0;
> +}
> +
> +char _license[] SEC("license") = "GPL";
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