Resolve race condition in Process.threads()

[li-dan]

Process.threads() has a race condition triggered when a thread exits after the open_binary() call and before the read() call. When this happens, the read() call raises ProcessLookupError.

Handle the race condition by catching ProcessLookupError from read() and treating the same as a FileNotFoundError from open_binary(). This is the same approach used in ppid_map().

Signed-off-by: Daniel Li daniel.li@deshaw.com

Summary

• OS: Linux
• Bug fix: yes
• Type: core
• Fixes: [Linux] Race condition in Process.threads() #2150

Description

Fix the race condition in Process.threads() using the same approach as ppid_map().

[giampaolo]

I see there is the same problem in open_files() method. While you're at it, could you please fix that one as well?
Thanks a lot

[li-dan]

Are you referring to these lines?

psutil/psutil/_pslinux.py

Lines 2213 to 2220 in 69b572e

	# Get file position and flags.
	file = "%s/%s/fdinfo/%s" % (
	self._procfs_path, self.pid, fd)
	try:
	with open_binary(file) as f:
	pos = int(f.readline().split()[1])
	flags = int(f.readline().split()[1], 8)
	except FileNotFoundError:

If the file descriptor disappears between the open_binary() and readline() calls, then readline() raises FileNotFoundError. So I believe that except FileNotFoundError is correct in open_files().

[giampaolo]

Yes I mean those lines. How do you know readline() can only raise FileNotFoundError? I think calling readline() should be like calling read().

[li-dan]

In my testing, it seems that .../fdinfo/... behaves differently from .../task/.... For example:

f1 = open("/etc/motd")
with open(f"/proc/{os.getpid()}/fdinfo/{f1.fileno()}", "rb") as f2:
    f1.close()
    f2.readline() # Raises FileNotFoundError

It's possible that some other Linux kernel will do something different, and it won't hurt either way, so I changed open_files() too.

[giampaolo]

Yeah let's just add it to be sure. Thanks for your PR.