[issue42509] Recursive calls crash interpreter when checking exceptions

[Mark Shannon]

Mark Shannon  added the comment:

Duplicate of 42500

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nosy: +Mark.Shannon
resolution:  -> duplicate
stage:  -> resolved
status: open -> closed

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[issue42509] Recursive calls crash interpreter when checking exceptions

[Dennis Sweeney]

Dennis Sweeney  added the comment:

sys.getrecursionlimit() returns whatever was passed to the most recent call of 
sys.setrecursionlimit(...), with some system default (here 1000).

Catching a RecursionError might be fine sometimes, but the issue is that 
Program 1 catches a RecursionError *and then keeps recursing more* rather than 
stopping.

I think it might have to be the responsibility of the Python user to make sure 
that if a RecursionError is to be caught, that the program can recover without 
making things much worse. It's my understanding that the extra buffer of +50 is 
to make sure that the programmer has room to stop the overflow and do any 
necessary cleanup [1].

If no attempt is made to clean up, then it seems reasonable to me that Python 
should crash, unless there's some idea of what could happen that I'm missing. 
The interpreter could allow arbitrary recursion during the cleanup until the C 
stack overflows, but that sort of defeats the point of the recursion checker. 
It could raise some new ExtraSuperRecurionError, but that doesn't fix anything: 
what if *that* error is caught ;) ?

[1] to get back to a recursion depth lower than some lower threshold: 
https://github.com/python/cpython/blob/master/Include/internal/pycore_ceval.h#L98

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[issue42509] Recursive calls crash interpreter when checking exceptions

[Xinmeng Xia]

Xinmeng Xia  added the comment:

But program like following program 3 will not cause any core dump, 
RecursionError is also being caught in this  Recursion.
program 3
def rec():
try:
rec()
except:
pass
rec()

Beside,I use sys.setrecursionlimit(80), and the program 1 still cause core 
dump.I print sys.getrecursionlimit(),the value is 1000. 80 is << 50 +1000, it 
shouldn't cause core dump.

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[issue42509] Recursive calls crash interpreter when checking exceptions

[Ronald Oussoren]

Ronald Oussoren  added the comment:

See also #42500

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nosy: +ronaldoussoren

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[issue42509] Recursive calls crash interpreter when checking exceptions

[Dennis Sweeney]

Dennis Sweeney  added the comment:

This might be the expected behavior. See https://bugs.python.org/issue25222

If you already caught a RecursionError and you keep recursing anyway, once you 
go 50 levels beyond sys.getrecursionlimit(), the interpreter crashes regardless 
of what is `except`ed. In /Python/ceval.c, there's this:

if (tstate->overflowed) {
if (tstate->recursion_depth > recursion_limit + 50) {
/* Overflowing while handling an overflow. Give up. */
Py_FatalError("Cannot recover from stack overflow.");
}
return 0;
}

In your Program 2, when the interpreter raises a `RecursionError`, it is raised 
normally and everything is fine.

In your Program 1, when the interpreter raises a `RecursionError`, it is 
`except`ed, so the interpreter thinks it's okay to keep going, and when it 
does, it raises more `RecursionError`s, which it keeps `except`ing, until it 
finally can't go any farther ( > 50 + sys.getrecursionlimit()), and has no 
option but to crash.

"Cannot recover from stack overflow." seems to make sense to me: when the 
interpreter tries to recover, the code won't let it.

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nosy: +Dennis Sweeney

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[issue42509] Recursive calls crash interpreter when checking exceptions

[Xinmeng Xia]

New submission from Xinmeng Xia :

The following program 1 can crash in Python 3. We have reproduce it in the 
Python version 3.5, 3.6, 3.7, 3.8, 3.9, 3.10. This bug seems to be similar to 
issue 36272, however, the tracking system shows issue 36272 has been fixed and 
the program 2, which triggers issue 36272, will not cause crash (“core dump”) 
in Python 3.8, 3.9, 3.10.
We have attached the stack trace in the end of this report.

Program 1: 

import logging

def rec():
try:
logging.error("foo")
except:
pass
rec()
rec()


Program 2: 

import logging

def rec():
logging.error("foo")
rec()
rec()
==
The error message is like following:
“
ERROR:root:foo
ERROR:root:foo
ERROR:root:foo
ERROR:root:foo
…
ERROR:root:foo
ERROR:root:foo
ERROR:root:foo
Fatal Python error: _Py_CheckRecursiveCall: Cannot recover from stack overflow.
Python runtime state: initialized

Current thread 0x7f0fa440b700 (most recent call first):
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 420 in 
usesTime
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 643 in 
usesTime
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 675 in 
format
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 938 in 
format
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 1094 in 
emit
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 963 in 
handle
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 1673 in 
callHandlers
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 1611 in 
handle
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 1601 in 
_log
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 1483 in 
error
  File "/usr/local/python310/lib/python3.10/logging/__init__.py", line 2080 in 
error
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 8 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
….
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  File "/home/xxm/Desktop/methodfuzzer/error/loggingtest.py", line 12 in rec
  ...
Aborted (core dumped)”

--
components: Interpreter Core
messages: 382111
nosy: xxm
priority: normal
severity: normal
status: open
title: Recursive calls crash interpreter when checking exceptions
type: crash
versions: Python 3.10

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