[PATCH 7/7] selftests: proc: Make sure wchan works when it exists

[Peter Zijlstra <peterz@infradead.org>]

From: Kees Cook <keescook@chromium.org>

This makes sure that wchan contains a sensible symbol when a process is
blocked. Specifically this calls the sleep() syscall, and expects the
architecture to have called schedule() from a function that has "sleep"
somewhere in its name. For example, on the architectures I tested
(x86_64, arm64, arm, mips, and powerpc) this is "hrtimer_nanosleep":

$ tools/testing/selftests/proc/proc-pid-wchan
ok: found 'sleep' in wchan 'hrtimer_nanosleep'

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20211008235504.2957528-1-keescook@chromium.org
---
 tools/testing/selftests/proc/Makefile         |    1 
 tools/testing/selftests/proc/proc-pid-wchan.c |   69 ++++++++++++++++++++++++++
 2 files changed, 70 insertions(+)
 create mode 100644 tools/testing/selftests/proc/proc-pid-wchan.c

--- a/tools/testing/selftests/proc/Makefile
+++ b/tools/testing/selftests/proc/Makefile
@@ -8,6 +8,7 @@ TEST_GEN_PROGS += fd-002-posix-eq
 TEST_GEN_PROGS += fd-003-kthread
 TEST_GEN_PROGS += proc-loadavg-001
 TEST_GEN_PROGS += proc-pid-vm
+TEST_GEN_PROGS += proc-pid-wchan
 TEST_GEN_PROGS += proc-self-map-files-001
 TEST_GEN_PROGS += proc-self-map-files-002
 TEST_GEN_PROGS += proc-self-syscall
--- /dev/null
+++ b/tools/testing/selftests/proc/proc-pid-wchan.c
@@ -0,0 +1,69 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Make sure that wchan returns a reasonable symbol when blocked.
+ */
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+#define perror_exit(str) do { perror(str); _exit(1); } while (0)
+
+int main(void)
+{
+	char buf[64];
+	pid_t child;
+	int sync[2], fd;
+
+	if (pipe(sync) < 0)
+		perror_exit("pipe");
+
+	child = fork();
+	if (child < 0)
+		perror_exit("fork");
+	if (child == 0) {
+		/* Child */
+		if (close(sync[0]) < 0)
+			perror_exit("child close sync[0]");
+		if (close(sync[1]) < 0)
+			perror_exit("child close sync[1]");
+		sleep(10);
+		_exit(0);
+	}
+	/* Parent */
+	if (close(sync[1]) < 0)
+		perror_exit("parent close sync[1]");
+	if (read(sync[0], buf, 1) != 0)
+		perror_exit("parent read sync[0]");
+
+	snprintf(buf, sizeof(buf), "/proc/%d/wchan", child);
+	fd = open(buf, O_RDONLY);
+	if (fd < 0) {
+		if (errno == ENOENT)
+			return 4;
+		perror_exit(buf);
+	}
+
+	memset(buf, 0, sizeof(buf));
+	if (read(fd, buf, sizeof(buf) - 1) < 1)
+		perror_exit(buf);
+	if (strstr(buf, "sleep") == NULL) {
+		fprintf(stderr, "FAIL: did not find 'sleep' in wchan '%s'\n", buf);
+		return 1;
+	}
+	printf("ok: found 'sleep' in wchan '%s'\n", buf);
+
+	if (kill(child, SIGKILL) < 0)
+		perror_exit("kill");
+	if (waitpid(child, NULL, 0) != child) {
+		fprintf(stderr, "waitpid: got the wrong child!?\n");
+		return 1;
+	}
+
+	return 0;
+}