[3.12] gh-122695: Fix double-free when using gc.get_referents with a freed _asyncio.FutureIter

[ZeroIntensity]

CC @vstinner, @douglas-raillard-arm

This is a (somewhat hacky) way to do it while keeping items in the freelist returned by gc.get_referents. The ideal solution would be to remove the traversal of the freelist all together, but that might be a breaking change (depending on how lisa relied on it).

• Issue: asyncio: FutureIter_dealloc() crashes with negative refcount #122695

[vstinner]

This change is wrong. A freelist is not storing objects but just raw memory.

module_traverse() should be modified to not visit the free list.

[bedevere-app]

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[ZeroIntensity]

(Hit the wrong button when copy-pasting the <gh-issue-number> shindig, my bad!)

[colesbury]

Do you want this in 3.13 as well?

[ZeroIntensity]

Do you want this in 3.13 as well?

Nope, this issue only occurs on 3.12.

[colesbury]

3.13 has the same underlying bug: module_traverse visits the free list, and the test case you added hangs (forever?) on 3.13.

[ZeroIntensity]

It's now just a removal of the traversal, as @vstinner suggested.

[ZeroIntensity]

3.13 has the same underlying bug: module_traverse visits the free list, and the test case you added hangs (forever?) on 3.13.

It does? I thought we tried this on 3.13 already. I guess this does go in 3.13 then.

[colesbury]

I thought we tried this on 3.13 already

I think someone confused 3.13 with the main branch (future 3.14 release)

[ZeroIntensity]

I thought we tried this on 3.13 already

I think someone confused 3.13 with the main branch (future 3.14 release)

Will make a PR for 3.13

[vstinner]

The issue should be fixed in the 3.13 branch and then backported automatically to 3.12. I close this PR in favor of #122837