netdev - Re: [PATCH bpf 3/3] selftests/bpf: retry tests that expect build-id

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Date:   Wed, 16 Jan 2019 17:49:27 +0000
From:   Song Liu <songliubraving@...com>
To:     Stanislav Fomichev <sdf@...gle.com>
CC:     Netdev <netdev@...r.kernel.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ast@...nel.org" <ast@...nel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf 3/3] selftests/bpf: retry tests that expect build-id



> On Jan 15, 2019, at 2:54 PM, Stanislav Fomichev <sdf@...gle.com> wrote:
> 
> While running test_progs in a loop I found out that I'm sometimes hitting
> "Didn't find expected build ID from the map" error.
> Looking at stack_map_get_build_id_offset() it seems that it is racy (by
> design) and can sometimes return BPF_STACK_BUILD_ID_IP (i.e. can't trylock
> current->mm->mmap_sem).
> 
> Let's retry this test a single time.
> 
> Fixes: 13790d1cc72c ("bpf: add selftest for stackmap with build_id in NMI context")
> Signed-off-by: Stanislav Fomichev <sdf@...gle.com>

Acked-by: Song Liu <songliubraving@...com>


> ---
> tools/testing/selftests/bpf/test_progs.c | 30 ++++++++++++++++++++++++
> 1 file changed, 30 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/test_progs.c b/tools/testing/selftests/bpf/test_progs.c
> index 126fc624290d..25f0083a9b2e 100644
> --- a/tools/testing/selftests/bpf/test_progs.c
> +++ b/tools/testing/selftests/bpf/test_progs.c
> @@ -1188,7 +1188,9 @@ static void test_stacktrace_build_id(void)
> 	int i, j;
> 	struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH];
> 	int build_id_matches = 0;
> +	int retry = 1;
> 
> +retry:
> 	err = bpf_prog_load(file, BPF_PROG_TYPE_TRACEPOINT, &obj, &prog_fd);
> 	if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
> 		goto out;
> @@ -1301,6 +1303,19 @@ static void test_stacktrace_build_id(void)
> 		previous_key = key;
> 	} while (bpf_map_get_next_key(stackmap_fd, &previous_key, &key) == 0);
> 
> +	/* stack_map_get_build_id_offset() is racy and sometimes can return
> +	 * BPF_STACK_BUILD_ID_IP instead of BPF_STACK_BUILD_ID_VALID;
> +	 * try it one more time.
> +	 */
> +	if (build_id_matches < 1 && retry--) {
> +		ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
> +		close(pmu_fd);
> +		bpf_object__close(obj);
> +		printf("%s:WARN:Didn't find expected build ID from the map, retrying\n",
> +		       __func__);
> +		goto retry;
> +	}
> +
> 	if (CHECK(build_id_matches < 1, "build id match",
> 		  "Didn't find expected build ID from the map\n"))
> 		goto disable_pmu;
> @@ -1341,7 +1356,9 @@ static void test_stacktrace_build_id_nmi(void)
> 	int i, j;
> 	struct bpf_stack_build_id id_offs[PERF_MAX_STACK_DEPTH];
> 	int build_id_matches = 0;
> +	int retry = 1;
> 
> +retry:
> 	err = bpf_prog_load(file, BPF_PROG_TYPE_PERF_EVENT, &obj, &prog_fd);
> 	if (CHECK(err, "prog_load", "err %d errno %d\n", err, errno))
> 		return;
> @@ -1436,6 +1453,19 @@ static void test_stacktrace_build_id_nmi(void)
> 		previous_key = key;
> 	} while (bpf_map_get_next_key(stackmap_fd, &previous_key, &key) == 0);
> 
> +	/* stack_map_get_build_id_offset() is racy and sometimes can return
> +	 * BPF_STACK_BUILD_ID_IP instead of BPF_STACK_BUILD_ID_VALID;
> +	 * try it one more time.
> +	 */
> +	if (build_id_matches < 1 && retry--) {
> +		ioctl(pmu_fd, PERF_EVENT_IOC_DISABLE);
> +		close(pmu_fd);
> +		bpf_object__close(obj);
> +		printf("%s:WARN:Didn't find expected build ID from the map, retrying\n",
> +		       __func__);
> +		goto retry;
> +	}
> +
> 	if (CHECK(build_id_matches < 1, "build id match",
> 		  "Didn't find expected build ID from the map\n"))
> 		goto disable_pmu;
> -- 
> 2.20.1.97.g81188d93c3-goog
>