[Linux] Race condition in Process.threads()

[li-dan]

Summary

• OS: Linux
• Architecture: 64bit
• Psutil version: 5.9.3
• Python version: 3.10.4
• Type: core

Description

Process.threads() has a race condition in this code:

psutil/psutil/_pslinux.py

Lines 2061 to 2068 in 69b572e

	try:
	with open_binary(fname) as f:
	st = f.read().strip()
	except FileNotFoundError:
	# no such file or directory; it means thread
	# disappeared on us
	hit_enoent = True
	continue

A thread may exit after the open_binary() call and before the read() call. In this case open_binary() will succeed but read() will raise ProcessLookupError.

I think this should be treated the same as FileNotFoundError from open_binary(), since in both cases it means the thread disappeared on us.

Here's some code I used to trigger the race condition:

import psutil
import random
import threading
import time

def noop():
    time.sleep(random.random() * 10)

def generate_threads():
    for _ in range(10):
        threads = []
        for _ in range(100):
            thread = threading.Thread(target=noop)
            thread.start()
            threads.append(thread)
        for thread in threads:
            thread.join()

t = threading.Thread(target=generate_threads)
t.start()

while t.is_alive():
    psutil.Process().threads()