gh-104252: Immortalize Py_EMPTY_KEYS by ericsnowcurrently · Pull Request #104253 · python/cpython

ericsnowcurrently · 2023-05-06T23:59:09Z

This was missed in gh-19474. It matters for with a per-interpreter GIL since PyDictKeysObject.dk_refcnt breaks isolation and leads to races.

cc @eduardo-elizondo

Issue: Immortalize Py_EMPTY_KEYS #104252

sunmy2019

There are other places with direct changes to dk_refcnt. They are not guarded.

cpython/Objects/dictobject.c

Line 639 in 4729383

dk->dk_refcnt = 1;

cpython/Objects/dictobject.c

Lines 822 to 828 in 4729383

    
               /* Since we copied the keys table we now have an extra reference 
        
                  in the system.  Manually call increment _Py_RefTotal to signal that 
        
                  we have it now; calling dictkeys_incref would be an error as 
        
                  keys->dk_refcnt is already set to 1 (after memcpy). */ 
        
           #ifdef Py_REF_DEBUG 
        
               _Py_IncRefTotal(_PyInterpreterState_GET()); 
        
           #endif

cpython/Objects/dictobject.c

Lines 1530 to 1538 in 4729383

    
                   // We can not use free_keys_object here because key's reference 
        
                   // are moved already. 
        
           #ifdef Py_REF_DEBUG 
        
                   _Py_DecRefTotal(_PyInterpreterState_GET()); 
        
           #endif 
        
                   if (oldkeys == Py_EMPTY_KEYS) { 
        
                       oldkeys->dk_refcnt--; 
        
                       assert(oldkeys->dk_refcnt > 0); 
        
                   }

Objects/dictobject.c

ericsnowcurrently · 2023-05-08T13:47:12Z

@sunmy2019, thanks for pointing out the other uses of dk_refcnt. I'll fix that.

[done]

Objects/dictobject.c

Include/internal/pycore_dict_state.h

Objects/dictobject.c

methane · 2023-05-09T01:56:53Z

Please remove these lines too:

cpython/Objects/dictobject.c

Line 849 in 58585a9

dictkeys_incref(Py_EMPTY_KEYS);

cpython/Objects/dictobject.c

Line 1347 in 58585a9

dictkeys_decref(interp, Py_EMPTY_KEYS);

And Move _Py_DecRefTotal() into if (oldkeys != Py_EMPTY_KEYS) block.

cpython/Objects/dictobject.c

Lines 1545 to 1548 in 58585a9

    
           #ifdef Py_REF_DEBUG 
        
                   _Py_DecRefTotal(_PyInterpreterState_GET()); 
        
           #endif 
        
                   if (oldkeys != Py_EMPTY_KEYS) {

ericsnowcurrently · 2023-05-09T03:35:51Z

Thanks for the feedback. I'll clean things up tomorrow.

bedevere-bot · 2023-05-09T18:51:10Z

🤖 New build scheduled with the buildbot fleet by @sunmy2019 for commit 5aabfd7 🤖

If you want to schedule another build, you need to add the 🔨 test-with-refleak-buildbots label again.

sunmy2019

LGTM! now it's much cleaner

ericsnowcurrently · 2023-05-10T13:42:49Z

Thanks for the reviews!

* main: pythonGH-102181: Improve specialization stats for SEND (pythonGH-102182) pythongh-103000: Optimise `dataclasses.asdict` for the common case (python#104364) pythongh-103538: Remove unused TK_AQUA code (pythonGH-103539) pythonGH-87695: Fix OSError from `pathlib.Path.glob()` (pythonGH-104292) pythongh-104263: Rely on Py_NAN and introduce Py_INFINITY (pythonGH-104202) pythongh-104010: Separate and improve docs for `typing.get_origin` and `typing.get_args` (python#104013) pythongh-101819: Adapt _io._BufferedIOBase_Type methods to Argument Clinic (python#104355) pythongh-103960: Dark mode: invert image brightness (python#103983) pythongh-104252: Immortalize Py_EMPTY_KEYS (pythongh-104253) pythongh-101819: Clean up _io windows console io after pythongh-104197 (python#104354) pythongh-101819: Harden _io init (python#104352) pythongh-103247: clear the module cache in a test in test_importlib/extensions/test_loader.py (pythonGH-104226) pythongh-103848: Adds checks to ensure that bracketed hosts found by urlsplit are of IPv6 or IPvFuture format (python#103849) pythongh-74895: adjust tests to work on Solaris (python#104326) pythongh-101819: Refactor _io in preparation for module isolation (python#104334) pythongh-90953: Don't use deprecated AST nodes in clinic.py (python#104322) pythongh-102327: Extend docs for "url" and "headers" parameters to HTTPConnection.request() pythongh-104328: Fix typo in ``typing.Generic`` multiple inheritance error message (python#104335)

* main: (27 commits) pythongh-87849: fix SEND specialization family definition (pythonGH-104268) pythongh-101819: Adapt _io.IOBase.seek and _io.IOBase.truncate to Argument Clinic (python#104384) pythongh-101819: Adapt _io._Buffered* methods to Argument Clinic (python#104367) pythongh-101819: Refactor `_io` futher in preparation for module isolation (python#104369) pythongh-101819: Adapt _io.TextIOBase methods to Argument Clinic (python#104383) pythongh-101117: Improve accuracy of sqlite3.Cursor.rowcount docs (python#104287) pythonGH-92184: Convert os.altsep to '/' in filenames when creating ZipInfo objects (python#92185) pythongh-104357: fix inlined comprehensions that close over iteration var (python#104368) pythonGH-90208: Suppress OSError exceptions from `pathlib.Path.glob()` (pythonGH-104141) pythonGH-102181: Improve specialization stats for SEND (pythonGH-102182) pythongh-103000: Optimise `dataclasses.asdict` for the common case (python#104364) pythongh-103538: Remove unused TK_AQUA code (pythonGH-103539) pythonGH-87695: Fix OSError from `pathlib.Path.glob()` (pythonGH-104292) pythongh-104263: Rely on Py_NAN and introduce Py_INFINITY (pythonGH-104202) pythongh-104010: Separate and improve docs for `typing.get_origin` and `typing.get_args` (python#104013) pythongh-101819: Adapt _io._BufferedIOBase_Type methods to Argument Clinic (python#104355) pythongh-103960: Dark mode: invert image brightness (python#103983) pythongh-104252: Immortalize Py_EMPTY_KEYS (pythongh-104253) pythongh-101819: Clean up _io windows console io after pythongh-104197 (python#104354) pythongh-101819: Harden _io init (python#104352) ...

eduardo-elizondo · 2023-06-19T15:32:56Z

Nice fix! I just got around to looking at this PR, it was weird thinking about the PyDictKeysObject since they were not PyObjects, so I just let them be. That being said, this LGTM specially if we are trying to share as much state as possible.

ericsnowcurrently added 2 commits May 6, 2023 17:55

Factor out _dict_state_INIT.

5bc2469

Immortalize Py_EMPTY_KEYS.

e472d94

ericsnowcurrently added the skip news label May 6, 2023

ericsnowcurrently requested a review from markshannon May 6, 2023 23:59

ericsnowcurrently requested a review from methane as a code owner May 6, 2023 23:59

bedevere-bot mentioned this pull request May 6, 2023

Immortalize Py_EMPTY_KEYS #104252

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bedevere-bot added the awaiting core review label May 6, 2023

ericsnowcurrently requested review from methane and removed request for methane May 6, 2023 23:59

sunmy2019 requested changes May 7, 2023

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ericsnowcurrently added 2 commits May 8, 2023 07:57

Handle other uses of dk_refcnt.

87351e0

Add a note.

f5da088

methane reviewed May 8, 2023

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ericsnowcurrently added 2 commits May 8, 2023 13:25

Drop an old line.

db8612f

Drop an unnecessary condition.

58585a9

methane reviewed May 9, 2023

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ericsnowcurrently added 4 commits May 9, 2023 10:11

Drop an unnecessary assert.

6b5c952

Do not bother inc/dec-refing Py_EMPTY_KEYS.

bdbce5f

Do not update Py_Reftotal for Py_EMPTY_KEYS.

aab493a

Clarify the comment about dictkeys_incref() and dictkeys_decref().

5aabfd7

ericsnowcurrently requested a review from sunmy2019 May 9, 2023 17:45

sunmy2019 added the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label May 9, 2023

bedevere-bot removed the 🔨 test-with-refleak-buildbots Test PR w/ refleak buildbots; report in status section label May 9, 2023

methane approved these changes May 10, 2023

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ericsnowcurrently merged commit b8f7ab5 into python:main May 10, 2023

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ericsnowcurrently deleted the immortalize-empty-keys branch May 10, 2023 13:28

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gh-104252: Immortalize Py_EMPTY_KEYS#104253

gh-104252: Immortalize Py_EMPTY_KEYS#104253
ericsnowcurrently merged 10 commits intopython:mainfrom
ericsnowcurrently:immortalize-empty-keys

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	/* Since we copied the keys table we now have an extra reference
	in the system. Manually call increment _Py_RefTotal to signal that
	we have it now; calling dictkeys_incref would be an error as
	keys->dk_refcnt is already set to 1 (after memcpy). */
	#ifdef Py_REF_DEBUG
	_Py_IncRefTotal(_PyInterpreterState_GET());
	#endif

	// We can not use free_keys_object here because key's reference
	// are moved already.
	#ifdef Py_REF_DEBUG
	_Py_DecRefTotal(_PyInterpreterState_GET());
	#endif
	if (oldkeys == Py_EMPTY_KEYS) {
	oldkeys->dk_refcnt--;
	assert(oldkeys->dk_refcnt > 0);
	}

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