From f80f88f0e2f2ef9cd805fad1bbf676b0ecd4b55c Mon Sep 17 00:00:00 2001 From: Florent Revest Date: Wed, 28 Apr 2021 17:25:01 +0200 Subject: selftests/bpf: Fix the snprintf test The BPF program for the snprintf selftest runs on all syscall entries. On busy multicore systems this can cause concurrency issues. For example it was observed that sometimes the userspace part of the test reads " 4 0000" instead of " 4 000" (extra '0' at the end) which seems to happen just before snprintf on another core sets end[-1] = '\0'. This patch adds a pid filter to the test to ensure that no bpf_snprintf() will write over the test's output buffers while the userspace reads the values. Fixes: c2e39c6bdc7e ("selftests/bpf: Add a series of tests for bpf_snprintf") Reported-by: Andrii Nakryiko Signed-off-by: Florent Revest Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20210428152501.1024509-1-revest@chromium.org --- tools/testing/selftests/bpf/prog_tests/snprintf.c | 2 ++ tools/testing/selftests/bpf/progs/test_snprintf.c | 5 +++++ 2 files changed, 7 insertions(+) (limited to 'tools') diff --git a/tools/testing/selftests/bpf/prog_tests/snprintf.c b/tools/testing/selftests/bpf/prog_tests/snprintf.c index a958c22aec75..dffbcaa1ec98 100644 --- a/tools/testing/selftests/bpf/prog_tests/snprintf.c +++ b/tools/testing/selftests/bpf/prog_tests/snprintf.c @@ -43,6 +43,8 @@ void test_snprintf_positive(void) if (!ASSERT_OK_PTR(skel, "skel_open")) return; + skel->bss->pid = getpid(); + if (!ASSERT_OK(test_snprintf__attach(skel), "skel_attach")) goto cleanup; diff --git a/tools/testing/selftests/bpf/progs/test_snprintf.c b/tools/testing/selftests/bpf/progs/test_snprintf.c index 951a0301c553..e35129bea0a0 100644 --- a/tools/testing/selftests/bpf/progs/test_snprintf.c +++ b/tools/testing/selftests/bpf/progs/test_snprintf.c @@ -5,6 +5,8 @@ #include #include +__u32 pid = 0; + char num_out[64] = {}; long num_ret = 0; @@ -42,6 +44,9 @@ int handler(const void *ctx) static const char str1[] = "str1"; static const char longstr[] = "longstr"; + if ((int)bpf_get_current_pid_tgid() != pid) + return 0; + /* Integer types */ num_ret = BPF_SNPRINTF(num_out, sizeof(num_out), "%d %u %x %li %llu %lX", -- cgit v1.2.3