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Message-ID: <CAEf4Bzbdg9MXDEz1fNXDPZfhe=_NAdLa6hT3M-EkLkycVdrW9w@mail.gmail.com>
Date: Fri, 19 Sep 2025 15:10:53 -0700
From: Andrii Nakryiko <andrii.nakryiko@...il.com>
To: Xu Kuohai <xukuohai@...weicloud.com>
Cc: bpf@...r.kernel.org, linux-kselftest@...r.kernel.org,
linux-kernel@...r.kernel.org, Alexei Starovoitov <ast@...nel.org>,
Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
Martin KaFai Lau <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>, Yonghong Song <yhs@...com>,
Song Liu <song@...nel.org>, John Fastabend <john.fastabend@...il.com>,
KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo <haoluo@...gle.com>,
Jiri Olsa <jolsa@...nel.org>, Mykola Lysenko <mykolal@...com>, Shuah Khan <shuah@...nel.org>,
Stanislav Fomichev <sdf@...ichev.me>, Willem de Bruijn <willemb@...gle.com>,
Jason Xing <kerneljasonxing@...il.com>, Paul Chaignon <paul.chaignon@...il.com>,
Tao Chen <chen.dylane@...ux.dev>, Kumar Kartikeya Dwivedi <memxor@...il.com>,
Martin Kelly <martin.kelly@...wdstrike.com>
Subject: Re: [PATCH bpf-next v2 2/3] selftests/bpf: Add test for overwrite
ring buffer
On Fri, Sep 5, 2025 at 8:13 AM Xu Kuohai <xukuohai@...weicloud.com> wrote:
>
> From: Xu Kuohai <xukuohai@...wei.com>
>
> Add test for overwiret mode ring buffer. The test creates a bpf ring
> buffer in overwrite mode, then repeatlly reserves and commits data
> to check if the ring buffer works as expected both before and after
> overwrite happens.
>
> Signed-off-by: Xu Kuohai <xukuohai@...wei.com>
> ---
> tools/testing/selftests/bpf/Makefile | 3 +-
> .../selftests/bpf/prog_tests/ringbuf.c | 74 ++++++++++++++
> .../bpf/progs/test_ringbuf_overwrite.c | 98 +++++++++++++++++++
> 3 files changed, 174 insertions(+), 1 deletion(-)
> create mode 100644 tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 11d2a368db3e..e6c18e201555 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -499,7 +499,8 @@ LINKED_SKELS := test_static_linked.skel.h linked_funcs.skel.h \
> LSKELS := fentry_test.c fexit_test.c fexit_sleep.c atomics.c \
> trace_printk.c trace_vprintk.c map_ptr_kern.c \
> core_kern.c core_kern_overflow.c test_ringbuf.c \
> - test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c
> + test_ringbuf_n.c test_ringbuf_map_key.c test_ringbuf_write.c \
> + test_ringbuf_overwrite.c
>
> # Generate both light skeleton and libbpf skeleton for these
> LSKELS_EXTRA := test_ksyms_module.c test_ksyms_weak.c kfunc_call_test.c \
> diff --git a/tools/testing/selftests/bpf/prog_tests/ringbuf.c b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> index d1e4cb28a72c..205a51c725a7 100644
> --- a/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> +++ b/tools/testing/selftests/bpf/prog_tests/ringbuf.c
> @@ -17,6 +17,7 @@
> #include "test_ringbuf_n.lskel.h"
> #include "test_ringbuf_map_key.lskel.h"
> #include "test_ringbuf_write.lskel.h"
> +#include "test_ringbuf_overwrite.lskel.h"
>
> #define EDONE 7777
>
> @@ -497,6 +498,77 @@ static void ringbuf_map_key_subtest(void)
> test_ringbuf_map_key_lskel__destroy(skel_map_key);
> }
>
> +static void ringbuf_overwrite_mode_subtest(void)
> +{
> + unsigned long size, len1, len2, len3, len4, len5;
> + unsigned long expect_avail_data, expect_prod_pos, expect_over_pos;
> + struct test_ringbuf_overwrite_lskel *skel;
> + int err;
> +
> + skel = test_ringbuf_overwrite_lskel__open();
> + if (!ASSERT_OK_PTR(skel, "skel_open"))
> + return;
> +
> + size = 0x1000;
> + len1 = 0x800;
> + len2 = 0x400;
> + len3 = size - len1 - len2 - BPF_RINGBUF_HDR_SZ * 3; /* 0x3e8 */
> + len4 = len3 - 8; /* 0x3e0 */
> + len5 = len3; /* retry with len3 */
> +
> + skel->maps.ringbuf.max_entries = size;
> + skel->rodata->LEN1 = len1;
> + skel->rodata->LEN2 = len2;
> + skel->rodata->LEN3 = len3;
> + skel->rodata->LEN4 = len4;
> + skel->rodata->LEN5 = len5;
> +
> + skel->bss->pid = getpid();
> +
> + err = test_ringbuf_overwrite_lskel__load(skel);
> + if (!ASSERT_OK(err, "skel_load"))
> + goto cleanup;
> +
> + err = test_ringbuf_overwrite_lskel__attach(skel);
> + if (!ASSERT_OK(err, "skel_attach"))
> + goto cleanup;
> +
> + syscall(__NR_getpgid);
> +
> + ASSERT_EQ(skel->bss->reserve1_fail, 0, "reserve 1");
> + ASSERT_EQ(skel->bss->reserve2_fail, 0, "reserve 2");
> + ASSERT_EQ(skel->bss->reserve3_fail, 1, "reserve 3");
> + ASSERT_EQ(skel->bss->reserve4_fail, 0, "reserve 4");
> + ASSERT_EQ(skel->bss->reserve5_fail, 0, "reserve 5");
> +
> + CHECK(skel->bss->ring_size != size,
> + "check_ring_size", "exp %lu, got %lu\n",
> + size, skel->bss->ring_size);
we don't use legacy CHECK() macros anymore, please use only ASSERT_xxx
> +
> + expect_avail_data = len2 + len4 + len5 + 3 * BPF_RINGBUF_HDR_SZ;
> + CHECK(skel->bss->avail_data != expect_avail_data,
> + "check_avail_size", "exp %lu, got %lu\n",
> + expect_avail_data, skel->bss->avail_data);
> +
> + CHECK(skel->bss->cons_pos != 0,
> + "check_cons_pos", "exp 0, got %lu\n",
> + skel->bss->cons_pos);
> +
> + expect_prod_pos = len1 + len2 + len4 + len5 + 4 * BPF_RINGBUF_HDR_SZ;
> + CHECK(skel->bss->prod_pos != expect_prod_pos,
> + "check_prod_pos", "exp %lu, got %lu\n",
> + expect_prod_pos, skel->bss->prod_pos);
> +
> + expect_over_pos = len1 + BPF_RINGBUF_HDR_SZ;
> + CHECK(skel->bss->over_pos != expect_over_pos,
> + "check_over_pos", "exp %lu, got %lu\n",
> + (unsigned long)expect_over_pos, skel->bss->over_pos);
> +
> + test_ringbuf_overwrite_lskel__detach(skel);
> +cleanup:
> + test_ringbuf_overwrite_lskel__destroy(skel);
> +}
> +
> void test_ringbuf(void)
> {
> if (test__start_subtest("ringbuf"))
> @@ -507,4 +579,6 @@ void test_ringbuf(void)
> ringbuf_map_key_subtest();
> if (test__start_subtest("ringbuf_write"))
> ringbuf_write_subtest();
> + if (test__start_subtest("ringbuf_overwrite_mode"))
> + ringbuf_overwrite_mode_subtest();
> }
> diff --git a/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c b/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c
> new file mode 100644
> index 000000000000..da89ba12a75c
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/test_ringbuf_overwrite.c
> @@ -0,0 +1,98 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/* Copyright (C) 2025. Huawei Technologies Co., Ltd */
> +
> +#include <linux/bpf.h>
> +#include <bpf/bpf_helpers.h>
> +#include "bpf_misc.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +struct {
> + __uint(type, BPF_MAP_TYPE_RINGBUF);
> + __uint(map_flags, BPF_F_OVERWRITE);
> +} ringbuf SEC(".maps");
> +
> +int pid;
> +
> +const volatile unsigned long LEN1;
> +const volatile unsigned long LEN2;
> +const volatile unsigned long LEN3;
> +const volatile unsigned long LEN4;
> +const volatile unsigned long LEN5;
> +
> +long reserve1_fail = 0;
> +long reserve2_fail = 0;
> +long reserve3_fail = 0;
> +long reserve4_fail = 0;
> +long reserve5_fail = 0;
> +
> +unsigned long avail_data = 0;
> +unsigned long ring_size = 0;
> +unsigned long cons_pos = 0;
> +unsigned long prod_pos = 0;
> +unsigned long over_pos = 0;
> +
> +SEC("fentry/" SYS_PREFIX "sys_getpgid")
> +int test_overwrite_ringbuf(void *ctx)
> +{
> + char *rec1, *rec2, *rec3, *rec4, *rec5;
> + int cur_pid = bpf_get_current_pid_tgid() >> 32;
> +
> + if (cur_pid != pid)
> + return 0;
> +
> + rec1 = bpf_ringbuf_reserve(&ringbuf, LEN1, 0);
> + if (!rec1) {
> + reserve1_fail = 1;
> + return 0;
> + }
> +
> + rec2 = bpf_ringbuf_reserve(&ringbuf, LEN2, 0);
> + if (!rec2) {
> + bpf_ringbuf_discard(rec1, 0);
> + reserve2_fail = 1;
> + return 0;
> + }
> +
> + rec3 = bpf_ringbuf_reserve(&ringbuf, LEN3, 0);
> + /* expect failure */
> + if (!rec3) {
> + reserve3_fail = 1;
> + } else {
> + bpf_ringbuf_discard(rec1, 0);
> + bpf_ringbuf_discard(rec2, 0);
> + bpf_ringbuf_discard(rec3, 0);
> + return 0;
> + }
> +
> + rec4 = bpf_ringbuf_reserve(&ringbuf, LEN4, 0);
> + if (!rec4) {
> + reserve4_fail = 1;
> + bpf_ringbuf_discard(rec1, 0);
> + bpf_ringbuf_discard(rec2, 0);
> + return 0;
> + }
> +
> + bpf_ringbuf_submit(rec1, 0);
> + bpf_ringbuf_submit(rec2, 0);
> + bpf_ringbuf_submit(rec4, 0);
> +
> + rec5 = bpf_ringbuf_reserve(&ringbuf, LEN5, 0);
> + if (!rec5) {
> + reserve5_fail = 1;
> + return 0;
> + }
> +
> + for (int i = 0; i < LEN3; i++)
> + rec5[i] = 0xdd;
> +
> + bpf_ringbuf_submit(rec5, 0);
> +
> + ring_size = bpf_ringbuf_query(&ringbuf, BPF_RB_RING_SIZE);
> + avail_data = bpf_ringbuf_query(&ringbuf, BPF_RB_AVAIL_DATA);
> + cons_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_CONS_POS);
> + prod_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_PROD_POS);
> + over_pos = bpf_ringbuf_query(&ringbuf, BPF_RB_OVER_POS);
> +
> + return 0;
> +}
> --
> 2.43.0
>
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