From e7679a5c820d0865d0900931a7341048d830917d Mon Sep 17 00:00:00 2001 From: Alexey Dobriyan Date: Fri, 7 Jun 2024 18:14:29 +0300 Subject: proc: test "Kthread:" field /proc/${pid}/status got Kthread field recently. Test that userspace program is not reported as kernel thread. Test that kernel thread is reported as kernel thread. Use kthreadd with pid 2 for this. Link: https://lkml.kernel.org/r/818c4c41-8668-4566-97a9-7254abf819ee@p183 Signed-off-by: Alexey Dobriyan Cc: Chunguang Wu Cc: Shuah Khan Signed-off-by: Andrew Morton --- tools/testing/selftests/proc/proc-2-is-kthread.c | 53 ++++++++++++++++++++++++ 1 file changed, 53 insertions(+) create mode 100644 tools/testing/selftests/proc/proc-2-is-kthread.c (limited to 'tools/testing/selftests/proc/proc-2-is-kthread.c') diff --git a/tools/testing/selftests/proc/proc-2-is-kthread.c b/tools/testing/selftests/proc/proc-2-is-kthread.c new file mode 100644 index 000000000000..f13668fb482e --- /dev/null +++ b/tools/testing/selftests/proc/proc-2-is-kthread.c @@ -0,0 +1,53 @@ +/* + * Copyright (c) 2024 Alexey Dobriyan + * + * Permission to use, copy, modify, and distribute this software for any + * purpose with or without fee is hereby granted, provided that the above + * copyright notice and this permission notice appear in all copies. + * + * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES + * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF + * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR + * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES + * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN + * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF + * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE. + */ +/* Test that kernel thread is reported as such. */ +#undef NDEBUG +#include +#include +#include +#include +#include + +int main(void) +{ + /* + * The following solutions don't really work: + * + * 1) jit kernel module which creates kernel thread: + * test becomes arch-specific, + * problems with mandatory module signing, + * problems with lockdown mode, + * doesn't work with CONFIG_MODULES=n at all, + * kthread creation API is formally unstable internal kernel API, + * need a mechanism to report test kernel thread's PID back, + * + * 2) ksoftirqd/0 and kswapd0 look like stable enough kernel threads, + * but their PIDs are unstable. + * + * Check against kthreadd which always seem to exist under pid 2. + */ + int fd = open("/proc/2/status", O_RDONLY); + assert(fd >= 0); + + char buf[4096]; + ssize_t rv = read(fd, buf, sizeof(buf)); + assert(0 <= rv && rv < sizeof(buf)); + buf[rv] = '\0'; + + assert(strstr(buf, "Kthread:\t1\n")); + + return 0; +} -- cgit v1.2.3