selftests/pidfd: first test for multi-threaded exec polling

Add first test for premature thread-group leader exit.

Link: https://lore.kernel.org/r/20250320-work-pidfs-thread_group-v4-2-da678ce805bf@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

diff --git a/tools/testing/selftests/pidfd/pidfd_info_test.c b/tools/testing/selftests/pidfd/pidfd_info_test.c
index 09bc4ae7aed55a175a26e03a1e695c4fc6410cd7..28a28ae4686a67474c4f62f4ab99d17f2db717df 100644 (file)
--- a/tools/testing/selftests/pidfd/pidfd_info_test.c
+++ b/tools/testing/selftests/pidfd/pidfd_info_test.c
@@ -236,7 +236,7 @@ static void *pidfd_info_pause_thread(void *arg)
 
 TEST_F(pidfd_info, thread_group)
 {
-       pid_t pid_leader, pid_thread;
+       pid_t pid_leader, pid_poller, pid_thread;
        pthread_t thread;
        int nevents, pidfd_leader, pidfd_thread, pidfd_leader_thread, ret;
        int ipc_sockets[2];
@@ -262,6 +262,35 @@ TEST_F(pidfd_info, thread_group)
                syscall(__NR_exit, EXIT_SUCCESS);
        }
 
+       /*
+        * Opening a PIDFD_THREAD aka thread-specific pidfd based on a
+        * thread-group leader must succeed.
+        */
+       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.
+                */
+               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));
@@ -275,12 +304,7 @@ TEST_F(pidfd_info, thread_group)
        pidfd_thread = sys_pidfd_open(pid_thread, PIDFD_THREAD);
        ASSERT_GE(pidfd_thread, 0);
 
-       /*
-        * Opening a PIDFD_THREAD aka thread-specific pidfd based on a
-        * thread-group leader must succeed.
-        */
-       pidfd_leader_thread = sys_pidfd_open(pid_leader, PIDFD_THREAD);
-       ASSERT_GE(pidfd_leader_thread, 0);
+       ASSERT_EQ(wait_for_pid(pid_poller), 0);
 
        /*
         * Note that pidfd_leader is a thread-group pidfd, so polling on it