libbpf CI has reported send_signal test is flaky although I am not able to reproduce it in my local environment. But I am able to reproduce with on-demand libbpf CI ([1]). Through code analysis, the following is possible reason. The failed subtest runs bpf program in softirq environment. Since bpf_send_signal() only sends to a fork of "test_progs" process. If the underlying current task is not "test_progs", bpf_send_signal() will not be triggered and the subtest will fail. To reduce the chances where the underlying process is not the intended one, this patch boosted scheduling priority to -20 (highest allowed by setpriority() call). And I did 10 runs with on-demand libbpf CI with this patch and I didn't observe any failures. [1] https://github.com/libbpf/libbpf/actions/workflows/ondemand.yml Signed-off-by: Yonghong Song <yhs@xxxxxx> --- .../selftests/bpf/prog_tests/send_signal.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/send_signal.c b/tools/testing/selftests/bpf/prog_tests/send_signal.c index 41e158ae888e..776916b61c40 100644 --- a/tools/testing/selftests/bpf/prog_tests/send_signal.c +++ b/tools/testing/selftests/bpf/prog_tests/send_signal.c @@ -1,5 +1,7 @@ // SPDX-License-Identifier: GPL-2.0 #include <test_progs.h> +#include <sys/time.h> +#include <sys/resource.h> #include "test_send_signal_kern.skel.h" int sigusr1_received = 0; @@ -37,12 +39,23 @@ static void test_send_signal_common(struct perf_event_attr *attr, } if (pid == 0) { + int old_prio; + /* install signal handler and notify parent */ signal(SIGUSR1, sigusr1_handler); close(pipe_c2p[0]); /* close read */ close(pipe_p2c[1]); /* close write */ + /* boost with a high priority so we got a higher chance + * that if an interrupt happens, the underlying task + * is this process. + */ + errno = 0; + old_prio = getpriority(PRIO_PROCESS, 0); + ASSERT_OK(errno, "getpriority"); + ASSERT_OK(setpriority(PRIO_PROCESS, 0, -20), "setpriority"); + /* notify parent signal handler is installed */ ASSERT_EQ(write(pipe_c2p[1], buf, 1), 1, "pipe_write"); @@ -58,6 +71,9 @@ static void test_send_signal_common(struct perf_event_attr *attr, /* wait for parent notification and exit */ ASSERT_EQ(read(pipe_p2c[0], buf, 1), 1, "pipe_read"); + /* restore the old priority */ + ASSERT_OK(setpriority(PRIO_PROCESS, 0, old_prio), "setpriority"); + close(pipe_c2p[1]); close(pipe_p2c[0]); exit(0); -- 2.30.2
