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Tue, 23 Jun 2020 22:27:41 +0000 Subject: Re: [PATCH bpf-next 3/3] selftests/bpf: add bpf_iter test with bpf_get_task_stack_trace() To: Song Liu CC: bpf , "netdev@vger.kernel.org" , "ast@kernel.org" , "daniel@iogearbox.net" , Kernel Team , "john.fastabend@gmail.com" , "kpsingh@chromium.org" References: <20200623070802.2310018-1-songliubraving@fb.com> <20200623070802.2310018-4-songliubraving@fb.com> <445e1e04-882f-7ff7-9bd4-ebcf679cebbb@fb.com> <78BB08A3-D049-4795-8702-470C5841062C@fb.com> From: Yonghong Song Message-ID: Date: Tue, 23 Jun 2020 15:27:39 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0) Gecko/20100101 Thunderbird/68.9.0 In-Reply-To: <78BB08A3-D049-4795-8702-470C5841062C@fb.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: BYAPR07CA0060.namprd07.prod.outlook.com (2603:10b6:a03:60::37) To BYAPR15MB4088.namprd15.prod.outlook.com (2603:10b6:a02:c3::18) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [IPv6:2620:10d:c085:21cf::1926] (2620:10d:c090:400::5:d956) by BYAPR07CA0060.namprd07.prod.outlook.com (2603:10b6:a03:60::37) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3109.22 via Frontend Transport; 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X-MS-Exchange-AntiSpam-MessageData: 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 X-MS-Exchange-CrossTenant-Network-Message-Id: 5085bf0a-edfc-49a3-6def-08d817c4a42c X-MS-Exchange-CrossTenant-OriginalArrivalTime: 23 Jun 2020 22:27:41.0268 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-CrossTenant-Id: 8ae927fe-1255-47a7-a2af-5f3a069daaa2 X-MS-Exchange-CrossTenant-MailboxType: HOSTED X-MS-Exchange-CrossTenant-UserPrincipalName: Fai327TXV1yi2++rbb3OaJXGaBlo70YHW8lEalx4qdmeQLhf2OflHlYlilevR2ie X-MS-Exchange-Transport-CrossTenantHeadersStamped: BYAPR15MB3303 X-OriginatorOrg: fb.com X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.216,18.0.687 definitions=2020-06-23_14:2020-06-23,2020-06-23 signatures=0 X-Proofpoint-Spam-Details: rule=fb_default_notspam policy=fb_default score=0 suspectscore=0 impostorscore=0 lowpriorityscore=0 spamscore=0 adultscore=0 malwarescore=0 mlxscore=0 phishscore=0 priorityscore=1501 mlxlogscore=999 bulkscore=0 clxscore=1015 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006120000 definitions=main-2006230148 X-FB-Internal: deliver Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 6/23/20 3:07 PM, Song Liu wrote: > > >> On Jun 23, 2020, at 11:57 AM, Yonghong Song wrote: >> >> >> >> On 6/23/20 12:08 AM, Song Liu wrote: >>> The new test is similar to other bpf_iter tests. >>> Signed-off-by: Song Liu >>> --- >>> .../selftests/bpf/prog_tests/bpf_iter.c | 17 +++++++ >>> .../selftests/bpf/progs/bpf_iter_task_stack.c | 50 +++++++++++++++++++ >>> 2 files changed, 67 insertions(+) >>> create mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c >>> diff --git a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c >>> index 87c29dde1cf96..baa83328f810d 100644 >>> --- a/tools/testing/selftests/bpf/prog_tests/bpf_iter.c >>> +++ b/tools/testing/selftests/bpf/prog_tests/bpf_iter.c >>> @@ -5,6 +5,7 @@ >>> #include "bpf_iter_netlink.skel.h" >>> #include "bpf_iter_bpf_map.skel.h" >>> #include "bpf_iter_task.skel.h" >>> +#include "bpf_iter_task_stack.skel.h" >>> #include "bpf_iter_task_file.skel.h" >>> #include "bpf_iter_test_kern1.skel.h" >>> #include "bpf_iter_test_kern2.skel.h" >>> @@ -106,6 +107,20 @@ static void test_task(void) >>> bpf_iter_task__destroy(skel); >>> } >>> +static void test_task_stack(void) >>> +{ >>> + struct bpf_iter_task_stack *skel; >>> + >>> + skel = bpf_iter_task_stack__open_and_load(); >>> + if (CHECK(!skel, "bpf_iter_task_stack__open_and_load", >>> + "skeleton open_and_load failed\n")) >>> + return; >>> + >>> + do_dummy_read(skel->progs.dump_task_stack); >>> + >>> + bpf_iter_task_stack__destroy(skel); >>> +} >>> + >>> static void test_task_file(void) >>> { >>> struct bpf_iter_task_file *skel; >>> @@ -392,6 +407,8 @@ void test_bpf_iter(void) >>> test_bpf_map(); >>> if (test__start_subtest("task")) >>> test_task(); >>> + if (test__start_subtest("task_stack")) >>> + test_task_stack(); >>> if (test__start_subtest("task_file")) >>> test_task_file(); >>> if (test__start_subtest("anon")) >>> diff --git a/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c >>> new file mode 100644 >>> index 0000000000000..4fc939e0fca77 >>> --- /dev/null >>> +++ b/tools/testing/selftests/bpf/progs/bpf_iter_task_stack.c >>> @@ -0,0 +1,50 @@ >>> +// SPDX-License-Identifier: GPL-2.0 >>> +/* Copyright (c) 2020 Facebook */ >>> +/* "undefine" structs in vmlinux.h, because we "override" them below */ >>> +#define bpf_iter_meta bpf_iter_meta___not_used >>> +#define bpf_iter__task bpf_iter__task___not_used >>> +#include "vmlinux.h" >>> +#undef bpf_iter_meta >>> +#undef bpf_iter__task >>> +#include >>> +#include >>> + >>> +char _license[] SEC("license") = "GPL"; >>> + >>> +struct bpf_iter_meta { >>> + struct seq_file *seq; >>> + __u64 session_id; >>> + __u64 seq_num; >>> +} __attribute__((preserve_access_index)); >>> + >>> +struct bpf_iter__task { >>> + struct bpf_iter_meta *meta; >>> + struct task_struct *task; >>> +} __attribute__((preserve_access_index)); >>> + >>> +#define MAX_STACK_TRACE_DEPTH 64 >>> +unsigned long entries[MAX_STACK_TRACE_DEPTH]; >>> + >>> +SEC("iter/task") >>> +int dump_task_stack(struct bpf_iter__task *ctx) >>> +{ >>> + struct seq_file *seq = ctx->meta->seq; >>> + struct task_struct *task = ctx->task; >>> + unsigned int i, num_entries; >>> + >>> + if (task == (void *)0) >>> + return 0; >>> + >>> + num_entries = bpf_get_task_stack_trace(task, entries, MAX_STACK_TRACE_DEPTH); >>> + >>> + BPF_SEQ_PRINTF(seq, "pid: %8u\n", task->pid); >>> + >>> + for (i = 0; i < MAX_STACK_TRACE_DEPTH; i++) { >>> + if (num_entries > i) >>> + BPF_SEQ_PRINTF(seq, "[<0>] %pB\n", (void *)entries[i]); >> >> We may have an issue on 32bit issue. >> On 32bit system, the following is called in the kernel >> + return stack_trace_save_tsk(task, (unsigned long *)entries, size, 0); >> it will pack addresses at 4 byte increment. >> But in BPF program, the reading is in 8 byte increment. > > Can we avoid potential issues by requiring size % 8 == 0? Or maybe round down > size to closest multiple of 8? This is what I mean: for bpf program: "long" means u64, so we allocate 64 * 8 buffer size and pass it to the helper in the helper, the address will be increased along sizeof(long), which is 4 for 32bit system. So address is recorded at buf, buf + 4, buf + 8, buf + 12, ... After the helper returns, the bpf program tries to retrieve the address at buf, buf + 8, buf + 16. The helper itself is okay. But BPF_SEQ_PRINTF above is wrong. Is this interpretation correct? > > Thanks, > Song >