fix(ci): epoll() on pidfd to wait for Firecracker exit

Currently, we use psutil.pid_exists in a loop with a timeout of 10
seconds. This is racy and indeed some times we hit it in our CI.

Substitute this mechanism with calling epoll() on the pidfd of the
process instead. This should deterministically block until the process
exits. If there's something else wrong, we will hit the pytest timeout.

Signed-off-by: Babis Chalios <[email protected]>

tests/framework/utils.py

@@ -7,6 +7,7 @@
 import os
 import platform
 import re
+import select
 import signal
 import stat
 import subprocess
@@ -450,16 +451,39 @@ def run_guest_cmd(ssh_connection, cmd, expected, use_json=False):
     assert stdout == expected
 
 
-@retry(wait=wait_fixed(1), stop=stop_after_attempt(10), reraise=True)
+def get_process_pidfd(pid):
+    """Get a pidfd file descriptor for the process with PID `pid`
+
+    Will return a pid file descriptor for the process with PID `pid` if it is
+    still alive. If the process has already exited it will return `None`.
+
+    Any other error while calling the system call, will raise an OSError
+    exception.
+    """
+    try:
+        pidfd = os.pidfd_open(pid)
+    except ProcessLookupError:
+        return None
+
+    return pidfd
+
+
 def wait_process_termination(p_pid):
     """Wait for a process to terminate.
 
-    Will return sucessfully if the process
+    Will return successfully if the process
     got indeed killed or raises an exception if the process
     is still alive after retrying several times.
     """
-    if psutil.pid_exists(p_pid):
-        raise Exception(f"[{p_pid}] process is still alive")
+    pidfd = get_process_pidfd(p_pid)
+
+    # If pidfd is None the process has already terminated
+    if pidfd is not None:
+        epoll = select.epoll()
+        epoll.register(pidfd, select.EPOLLIN)
+        # This will return once the process exits
+        epoll.poll()
+        os.close(pidfd)
 
 
 def get_firecracker_version_from_toml():