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[3.10] bpo-44449: faulthandler don't modify frame refcnt#27850

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vstinner merged 1 commit intopython:3.10from
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Aug 30, 2021
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[3.10] bpo-44449: faulthandler don't modify frame refcnt#27850
vstinner merged 1 commit intopython:3.10from
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@vstinner vstinner commented Aug 20, 2021 •
edited by bedevere-bot
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Fix a crash in the signal handler of the faulthandler module: no
longer modify the reference count of frame objects.

https://bugs.python.org/issue44449

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bpo-44449: faulthandler don't modify frame refcnt
f8dfd90 
Fix a crash in the signal handler of the faulthandler module: no
longer modify the reference count of frame objects.
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LGTM. I'm not sure how to write a test for this though.

BTW, to make bedevere/maintenance-branch-pr — Not a valid maintenance branch PR title. test pass, you can rename issue title to [3.10] bpo...

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markshannon commented Aug 21, 2021

I don't think there is anything wring with _Py_DumpTraceback. The problem is that we are calling it from the fault handler.
Since the VM is not in a valid state (or there wouldn't be a fault), we shouldn't call any API functions from the fault handler.

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markshannon commented Aug 21, 2021

I hadn't realized that this is for 3.10. It should be OK it that case.

@vstinner vstinner changed the title bpo-44449: faulthandler don't modify frame refcnt [3.10] bpo-44449: faulthandler don't modify frame refcnt Aug 30, 2021
@vstinner vstinner merged commit fe997e1 into python:3.10 Aug 30, 2021
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miss-islington commented Aug 30, 2021

Thanks @vstinner for the PR 🌮🎉.. I'm working now to backport this PR to: 3.9.
🐍🍒⛏🤖

@vstinner vstinner deleted the traceback_refcnt branch August 30, 2021 13:24
miss-islington pushed a commit to miss-islington/cpython that referenced this pull request Aug 30, 2021
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bpo-44449: faulthandler don't modify frame refcnt (pythonGH-27850)
cb28ba8 
Fix a crash in the signal handler of the faulthandler module: no
longer modify the reference count of frame objects.
(cherry picked from commit fe997e1)

Co-authored-by: Victor Stinner <[email protected]>
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bedevere-bot commented Aug 30, 2021

GH-28066 is a backport of this pull request to the 3.9 branch.

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vstinner commented Aug 30, 2021

@markshannon: In the main branch, dump_traceback() reads tstate->frame and frame->previous.

Since the VM is not in a valid state (or there wouldn't be a fault), we shouldn't call any API functions from the fault handler.

Right. Hopefully, in my experience, faulthandler is also to dump the traceback in almost all cases, even if something really bad happens. Anyway, Python is already exiting with a "fatal error", so it's not a big deal if it triggers a new crash :-D

miss-islington added a commit that referenced this pull request Aug 30, 2021
@miss-islington @vstinner
bpo-44449: faulthandler don't modify frame refcnt (GH-27850)
720aef4 
Fix a crash in the signal handler of the faulthandler module: no
longer modify the reference count of frame objects.
(cherry picked from commit fe997e1)

Co-authored-by: Victor Stinner <[email protected]>
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