Ensure that during a multi-threaded exec and premature thread-group
leader exit no exit notification is generated.
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
---
tools/testing/selftests/pidfd/pidfd_info_test.c | 72 ++++++++++++++++---------
1 file changed, 48 insertions(+), 24 deletions(-)
diff --git a/tools/testing/selftests/pidfd/pidfd_info_test.c b/tools/testing/selftests/pidfd/pidfd_info_test.c
index 28a28ae4686a..4169780c9e55 100644
--- a/tools/testing/selftests/pidfd/pidfd_info_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_info_test.c
@@ -413,7 +413,7 @@ static void *pidfd_info_thread_exec(void *arg)
TEST_F(pidfd_info, thread_group_exec)
{
- pid_t pid_leader, pid_thread;
+ pid_t pid_leader, pid_poller, pid_thread;
pthread_t thread;
int nevents, pidfd_leader, pidfd_leader_thread, pidfd_thread, ret;
int ipc_sockets[2];
@@ -439,6 +439,37 @@ TEST_F(pidfd_info, thread_group_exec)
syscall(__NR_exit, EXIT_SUCCESS);
}
+ /* Open a thread-specific pidfd for the thread-group leader. */
+ pidfd_leader_thread = sys_pidfd_open(pid_leader, PIDFD_THREAD);
+ ASSERT_GE(pidfd_leader_thread, 0);
+
+ pid_poller = fork();
+ ASSERT_GE(pid_poller, 0);
+ if (pid_poller == 0) {
+ /*
+ * We can't poll and wait for the old thread-group
+ * leader to exit using a thread-specific pidfd. The
+ * thread-group leader exited prematurely and
+ * notification is delayed until all subthreads have
+ * exited.
+ *
+ * When the thread has execed it will taken over the old
+ * thread-group leaders struct pid. Calling poll after
+ * the thread execed will thus block again because a new
+ * thread-group has started.
+ */
+ fds.events = POLLIN;
+ fds.fd = pidfd_leader_thread;
+ nevents = poll(&fds, 1, 10000 /* wait 5 seconds */);
+ if (nevents != 0)
+ _exit(EXIT_FAILURE);
+ if (fds.revents & POLLIN)
+ _exit(EXIT_FAILURE);
+ if (fds.revents & POLLHUP)
+ _exit(EXIT_FAILURE);
+ _exit(EXIT_SUCCESS);
+ }
+
/* Retrieve the tid of the thread. */
EXPECT_EQ(close(ipc_sockets[1]), 0);
ASSERT_EQ(read_nointr(ipc_sockets[0], &pid_thread, sizeof(pid_thread)), sizeof(pid_thread));
@@ -447,33 +478,12 @@ TEST_F(pidfd_info, thread_group_exec)
pidfd_thread = sys_pidfd_open(pid_thread, PIDFD_THREAD);
ASSERT_GE(pidfd_thread, 0);
- /* Open a thread-specific pidfd for the thread-group leader. */
- pidfd_leader_thread = sys_pidfd_open(pid_leader, PIDFD_THREAD);
- ASSERT_GE(pidfd_leader_thread, 0);
-
- /*
- * We can poll and wait for the old thread-group leader to exit
- * using a thread-specific pidfd.
- *
- * This only works until the thread has execed. When the thread
- * has execed it will have taken over the old thread-group
- * leaders struct pid. Calling poll after the thread execed will
- * thus block again because a new thread-group has started (Yes,
- * it's fscked.).
- */
- fds.events = POLLIN;
- fds.fd = pidfd_leader_thread;
- nevents = poll(&fds, 1, -1);
- ASSERT_EQ(nevents, 1);
- /* The thread-group leader has exited. */
- ASSERT_TRUE(!!(fds.revents & POLLIN));
- /* The thread-group leader hasn't been reaped. */
- ASSERT_FALSE(!!(fds.revents & POLLHUP));
-
/* Now that we've opened a thread-specific pidfd the thread can exec. */
ASSERT_EQ(write_nointr(ipc_sockets[0], &pid_thread, sizeof(pid_thread)), sizeof(pid_thread));
EXPECT_EQ(close(ipc_sockets[0]), 0);
+ ASSERT_EQ(wait_for_pid(pid_poller), 0);
+
/* Wait until the kernel has SIGKILLed the thread. */
fds.events = POLLHUP;
fds.fd = pidfd_thread;
@@ -506,6 +516,20 @@ TEST_F(pidfd_info, thread_group_exec)
/* Take down the thread-group leader. */
EXPECT_EQ(sys_pidfd_send_signal(pidfd_leader, SIGKILL, NULL, 0), 0);
+
+ /*
+ * Afte the exec we're dealing with an empty thread-group so now
+ * we must see an exit notification on the thread-specific pidfd
+ * for the thread-group leader as there's no subthread that can
+ * revive the struct pid.
+ */
+ fds.events = POLLIN;
+ fds.fd = pidfd_leader_thread;
+ nevents = poll(&fds, 1, -1);
+ ASSERT_EQ(nevents, 1);
+ ASSERT_TRUE(!!(fds.revents & POLLIN));
+ ASSERT_FALSE(!!(fds.revents & POLLHUP));
+
EXPECT_EQ(sys_waitid(P_PIDFD, pidfd_leader, NULL, WEXITED), 0);
/* Retrieve exit information for the thread-group leader. */
--
2.47.2
