Free threading locking issues in listobject.c

@mpage

Bug report

In #127524, @mpage suggested adding an assert to check that the list object is locked when calling ensure_shared_on_resize. This uncovers a few more locking issues.

Additionally, we may return out of the critical section without unlocking here:

cpython/Objects/listobject.c

Lines 956 to 964 in c7dec02

    
           Py_BEGIN_CRITICAL_SECTION(a); 
        
           Py_ssize_t n = PyList_GET_SIZE(a); 
        
           PyObject *copy = list_slice_lock_held(a, 0, n); 
        
           if (copy == NULL) { 
        
               return -1; 
        
           } 
        
           ret = list_ass_slice_lock_held(a, ilow, ihigh, copy); 
        
           Py_DECREF(copy); 
        
           Py_END_CRITICAL_SECTION();

Linked PRs

Ah.. it's my fault, I will take a look at it

@corona10

Thanks @corona10. I started some work on this (but didn't finish) yesterday. Here's what I had in case it's helpful:

colesbury@49268ba

Ah in that case please go ahead

pythongh-127536: Add missing locks in listobject.c

gh-127536: Add missing locks in listobject.c (GH-127580)

[3.13] pythongh-127536: Add missing locks in listobject.c (pythonGH-1…

[3.13] gh-127536: Add missing locks in listobject.c (GH-127580) (GH-1…

@colesbury

@colesbury Are the build bot failures possibly related to that one or not? if not, I think we can close this one.

I think the buildbot failures are unrelated. The other s390x 3.13 buildbots are passing. https://buildbot.python.org/#/builders/1469 is passing, but the runs slowed down (including on test_site) around the same time, but on the following commit, which makes me think some sort of network issue or problem with the machine.

pythongh-127536: Add missing locks in listobject.c (pythonGH-127580)

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Free threading locking issues in `listobject.c` #127536

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	Py_BEGIN_CRITICAL_SECTION(a);
	Py_ssize_t n = PyList_GET_SIZE(a);
	PyObject *copy = list_slice_lock_held(a, 0, n);
	if (copy == NULL) {
	return -1;
	}
	ret = list_ass_slice_lock_held(a, ilow, ihigh, copy);
	Py_DECREF(copy);
	Py_END_CRITICAL_SECTION();

Free threading locking issues in listobject.c #127536

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corona10 commented on Dec 3, 2024

colesbury commented on Dec 3, 2024

corona10 commented on Dec 3, 2024

picnixz commented on Dec 5, 2024

colesbury commented on Dec 5, 2024

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Free threading locking issues in `listobject.c` #127536