selftests/pidfd: add tests for PIDFD_SELF_*

Add tests to assert that PIDFD_SELF* correctly refers to the current
thread and process.

We explicitly test pidfd_send_signal(), however We defer testing of
mm-specific functionality which uses pidfd, namely process_madvise() and
process_mrelease() to mm testing (though note the latter can not be
sensibly tested as it would require the testing process to be dying).

We also correct the pidfd_open_test.c fields which refer to .request_mask
whereas the UAPI header refers to .mask, which otherwise break the import
of the UAPI header.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Link: https://lore.kernel.org/r/7ab0e48b26ba53abf7b703df2dd11a2e99b8efb2.1738268370.git.lorenzo.stoakes@oracle.com
Reviewed-by: Shakeel Butt <shakeel.butt@linux.dev>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: ljskernel

tools/testing/selftests/pidfd/pidfd_open_test.c

@@ -31,7 +31,7 @@
 #define PIDFD_INFO_CGROUPID		(1UL << 0)
 
 struct pidfd_info {
-	__u64 request_mask;
+	__u64 mask;
 	__u64 cgroupid;
 	__u32 pid;
 	__u32 tgid;
@@ -148,7 +148,7 @@ static pid_t get_pid_from_fdinfo_file(int pidfd, const char *key, size_t keylen)
 int main(int argc, char **argv)
 {
 	struct pidfd_info info = {
-		.request_mask = PIDFD_INFO_CGROUPID,
+		.mask = PIDFD_INFO_CGROUPID,
 	};
 	int pidfd = -1, ret = 1;
 	pid_t pid;
@@ -227,7 +227,7 @@ int main(int argc, char **argv)
 			       getegid(), info.sgid);
 		goto on_error;
 	}
-	if ((info.request_mask & PIDFD_INFO_CGROUPID) && info.cgroupid == 0) {
+	if ((info.mask & PIDFD_INFO_CGROUPID) && info.cgroupid == 0) {
 		ksft_print_msg("cgroupid should not be 0 when PIDFD_INFO_CGROUPID is set\n");
 		goto on_error;
 	}

tools/testing/selftests/pidfd/pidfd_test.c

@@ -42,12 +42,41 @@ static pid_t pidfd_clone(int flags, int *pidfd, int (*fn)(void *))
 #endif
 }
 
-static int signal_received;
+static pthread_t signal_received;
 
 static void set_signal_received_on_sigusr1(int sig)
 {
 	if (sig == SIGUSR1)
-		signal_received = 1;
+		signal_received = pthread_self();
+}
+
+static int send_signal(int pidfd)
+{
+	int ret = 0;
+
+	if (sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0) < 0) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
+	if (signal_received != pthread_self()) {
+		ret = -EINVAL;
+		goto exit;
+	}
+
+exit:
+	signal_received = 0;
+	return ret;
+}
+
+static void *send_signal_worker(void *arg)
+{
+	int pidfd = (int)(intptr_t)arg;
+	int ret;
+
+	/* We forward any errors for the caller to handle. */
+	ret = send_signal(pidfd);
+	return (void *)(intptr_t)ret;
 }
 
 /*
@@ -56,8 +85,11 @@ static void set_signal_received_on_sigusr1(int sig)
  */
 static int test_pidfd_send_signal_simple_success(void)
 {
-	int pidfd, ret;
+	int pidfd;
 	const char *test_name = "pidfd_send_signal send SIGUSR1";
+	pthread_t thread;
+	void *thread_res;
+	int err;
 
 	if (!have_pidfd_send_signal) {
 		ksft_test_result_skip(
@@ -66,25 +98,45 @@ static int test_pidfd_send_signal_simple_success(void)
 		return 0;
 	}
 
+	signal(SIGUSR1, set_signal_received_on_sigusr1);
+
+	/* Try sending a signal to ourselves via /proc/self. */
 	pidfd = open("/proc/self", O_DIRECTORY | O_CLOEXEC);
 	if (pidfd < 0)
 		ksft_exit_fail_msg(
 			"%s test: Failed to open process file descriptor\n",
 			test_name);
+	err = send_signal(pidfd);
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on sending pidfd signal\n",
+			test_name, err);
+	close(pidfd);
 
-	signal(SIGUSR1, set_signal_received_on_sigusr1);
+	/* Now try the same thing only using PIDFD_SELF_THREAD_GROUP. */
+	err = send_signal(PIDFD_SELF_THREAD_GROUP);
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on PIDFD_SELF_THREAD_GROUP signal\n",
+			test_name, err);
 
-	ret = sys_pidfd_send_signal(pidfd, SIGUSR1, NULL, 0);
-	close(pidfd);
-	if (ret < 0)
-		ksft_exit_fail_msg("%s test: Failed to send signal\n",
+	/*
+	 * Now try the same thing in a thread and assert thread ID is equal to
+	 * worker thread ID.
+	 */
+	if (pthread_create(&thread, NULL, send_signal_worker,
+			   (void *)(intptr_t)PIDFD_SELF_THREAD))
+		ksft_exit_fail_msg("%s test: Failed to create thread\n",
 				   test_name);
-
-	if (signal_received != 1)
-		ksft_exit_fail_msg("%s test: Failed to receive signal\n",
+	if (pthread_join(thread, &thread_res))
+		ksft_exit_fail_msg("%s test: Failed to join thread\n",
 				   test_name);
+	err = (int)(intptr_t)thread_res;
+	if (err)
+		ksft_exit_fail_msg(
+			"%s test: Error %d on PIDFD_SELF_THREAD signal\n",
+			test_name, err);
 
-	signal_received = 0;
 	ksft_test_result_pass("%s test: Sent signal\n", test_name);
 	return 0;
 }