[LTP] [PATCH 5/5] fanotify21: Add FAN_REPORT_TID pidfd coverage

[AnonymeMeow]

Add a test case that generates an event from a thread. Without
FAN_REPORT_TID, the reported pidfd is expected to refer to the thread
group leader. With FAN_REPORT_TID, it is expected to refer to the
triggering thread. Keep the event thread alive until the reported pidfd
is verified, because pidfd fdinfo reports Pid: -1 after the thread
exits.

Signed-off-by: AnonymeMeow <anonymemeow@gmail.com>
---
 .../kernel/syscalls/fanotify/fanotify21.c     | 47 ++++++++++++++++++-
 1 file changed, 46 insertions(+), 1 deletion(-)

diff --git a/testcases/kernel/syscalls/fanotify/fanotify21.c b/testcases/kernel/syscalls/fanotify/fanotify21.c
index fd43c8c1c..8a5b35334 100644
--- a/testcases/kernel/syscalls/fanotify/fanotify21.c
+++ b/testcases/kernel/syscalls/fanotify/fanotify21.c
@@ -24,6 +24,7 @@
 #include "tst_test.h"
 #include "tst_safe_stdio.h"
 #include "tst_safe_macros.h"
+#include "tst_safe_pthread.h"
 #include "lapi/pidfd.h"
 
 #ifdef HAVE_SYS_FANOTIFY_H
@@ -46,6 +47,7 @@ struct pidfd_fdinfo_t {
 
 static struct test_case_t {
 	char *name;
+	int event_by_thread;
 	int want_pidfd_err;
 	int remount_ro;
 } test_cases[] = {
@@ -53,15 +55,24 @@ static struct test_case_t {
 		"return a valid pidfd for event created by self",
 		0,
 		0,
+		0,
+	},
+	{
+		"return a valid pidfd for event created by thread",
+		1,
+		0,
+		0,
 	},
 	{
 		"return invalid pidfd for reader in descendant PID namespace",
+		0,
 		1,
 		0,
 	},
 	{
 		"fail to open rw fd for event created on read-only mount",
 		0,
+		0,
 		1,
 	},
 };
@@ -107,6 +118,26 @@ static void generate_event(void)
 	SAFE_CLOSE(fd);
 }
 
+static void *generate_event_pthread(void *args LTP_ATTRIBUTE_UNUSED)
+{
+	generate_event();
+	TST_CHECKPOINT_WAIT(0);
+	return NULL;
+}
+
+static pthread_t event_thread_create(void)
+{
+	pthread_t pthread_id;
+	SAFE_PTHREAD_CREATE(&pthread_id, NULL, generate_event_pthread, NULL);
+	return pthread_id;
+}
+
+static void event_thread_join(pthread_t pthread_id)
+{
+	TST_CHECKPOINT_WAKE(0);
+	SAFE_PTHREAD_JOIN(pthread_id, NULL);
+}
+
 static const char *test_variant_name(void)
 {
 	switch (tst_variant) {
@@ -164,6 +195,7 @@ static void do_test(unsigned int num)
 	int nopidfd_err = tc->want_pidfd_err ?
 			  (TST_VARIANT_FD_ERROR ? -ESRCH : FAN_NOPIDFD) : 0;
 	int fd_err = (tc->remount_ro && TST_VARIANT_FD_ERROR) ? -EROFS : 0;
+	pthread_t event_thread;
 	pid_t reader_pid;
 	int reader_exit_status;
 
@@ -185,7 +217,16 @@ static void do_test(unsigned int num)
 	SAFE_MOUNT("none", MOUNT_PATH, "none", MS_BIND | MS_REMOUNT |
 		   (tc->remount_ro ? MS_RDONLY : 0), NULL);
 
-	generate_event();
+	/*
+	 * Generate the event by either self or a thread. Event generation in
+	 * a thread is done so that in FAN_REPORT_TID mode the pidfd can be
+	 * verified to refer to the tid, not the tgid. The thread waits until
+	 * the pidfd is verified before exiting.
+	 */
+	if (tc->event_by_thread)
+		event_thread = event_thread_create();
+	else
+		generate_event();
 
 	/*
 	 * Read the event in either self or a child process in a descendant
@@ -348,6 +389,9 @@ next_event:
 
 	if (tc->want_pidfd_err)
 		exit(0);
+
+	if (tc->event_by_thread)
+		event_thread_join(event_thread);
 }
 
 static void do_cleanup(void)
@@ -370,6 +414,7 @@ static struct tst_test test = {
 	.mount_device = 1,
 	.mntpoint = MOUNT_PATH,
 	.forks_child = 1,
+	.needs_checkpoints = 1,
 };
 
 #else
-- 
2.54.0