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Message-ID: <818c4c41-8668-4566-97a9-7254abf819ee@p183>
Date: Fri, 7 Jun 2024 18:14:29 +0300
From: Alexey Dobriyan <adobriyan@...il.com>
To: akpm@...ux-foundation.org
Cc: linux-kernel@...r.kernel.org
Subject: [PATCH] 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.
Signed-off-by: Alexey Dobriyan <adobriyan@...il.com>
---
tools/testing/selftests/proc/.gitignore | 2
tools/testing/selftests/proc/Makefile | 2
tools/testing/selftests/proc/proc-2-is-kthread.c | 53 ++++++++++++++++++
tools/testing/selftests/proc/proc-self-isnt-kthread.c | 37 ++++++++++++
4 files changed, 94 insertions(+)
--- a/tools/testing/selftests/proc/.gitignore
+++ b/tools/testing/selftests/proc/.gitignore
@@ -2,6 +2,7 @@
/fd-001-lookup
/fd-002-posix-eq
/fd-003-kthread
+/proc-2-is-kthread
/proc-fsconfig-hidepid
/proc-loadavg-001
/proc-multiple-procfs
@@ -9,6 +10,7 @@
/proc-pid-vm
/proc-self-map-files-001
/proc-self-map-files-002
+/proc-self-isnt-kthread
/proc-self-syscall
/proc-self-wchan
/proc-subset-pid
--- a/tools/testing/selftests/proc/Makefile
+++ b/tools/testing/selftests/proc/Makefile
@@ -7,11 +7,13 @@ TEST_GEN_PROGS :=
TEST_GEN_PROGS += fd-001-lookup
TEST_GEN_PROGS += fd-002-posix-eq
TEST_GEN_PROGS += fd-003-kthread
+TEST_GEN_PROGS += proc-2-is-kthread
TEST_GEN_PROGS += proc-loadavg-001
TEST_GEN_PROGS += proc-empty-vm
TEST_GEN_PROGS += proc-pid-vm
TEST_GEN_PROGS += proc-self-map-files-001
TEST_GEN_PROGS += proc-self-map-files-002
+TEST_GEN_PROGS += proc-self-isnt-kthread
TEST_GEN_PROGS += proc-self-syscall
TEST_GEN_PROGS += proc-self-wchan
TEST_GEN_PROGS += proc-subset-pid
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-2-is-kthread.c
@@ -0,0 +1,53 @@
+/*
+ * Copyright (c) 2024 Alexey Dobriyan <adobriyan@...il.com>
+ *
+ * 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 <assert.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+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;
+}
new file mode 100644
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-self-isnt-kthread.c
@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2024 Alexey Dobriyan <adobriyan@...il.com>
+ *
+ * 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 userspace program is not kernel thread. */
+#undef NDEBUG
+#include <assert.h>
+#include <fcntl.h>
+#include <string.h>
+#include <unistd.h>
+
+int main(void)
+{
+ int fd = open("/proc/self/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';
+
+ /* This test is very much not kernel thread. */
+ assert(strstr(buf, "Kthread:\t0\n"));
+
+ return 0;
+}
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