gh-151436: Fix missing tstate->last_profiled_frame updates

[maurycy]

Please see #151436 for more details.

The issue is fixed, drv_a is back:

def gen():
    while True:
        n = yield
        sum(range(n))

g = gen()
next(g)

def drv_a(): g.send(500)
def drv_b(): g.send(50000)

while True:
    drv_a(); drv_b()

2026-06-13T11:47:41.099330000+0200 maurycy@gimel /Users/maurycy/work/cpython (gh-151436 4eab5a0?) % sudo ./python.exe -m profiling.sampling run --collapsed -o /tmp/stacks.txt -d  10 genrepro.py&& cat /tmp/stacks.txt
Captured 10,000 samples in 10.00 seconds
Sample rate: 999.99 samples/sec
Error rate: 0.01
Collapsed stack output written to /tmp/stacks.txt
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13;genrepro.py:drv_b:10;genrepro.py:gen:4 9945
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13;genrepro.py:drv_a:9;genrepro.py:gen:4 48
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13;genrepro.py:drv_b:10;genrepro.py:gen:3 3
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13 1
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13;genrepro.py:drv_a:9 1
tid:13799271;<frozen runpy>:_run_module_as_main:201;<frozen runpy>:_run_code:87;genrepro.py:<module>:13;genrepro.py:drv_b:10 1
2026-06-13T11:47:51.429974000+0200 maurycy@gimel /Users/maurycy/work/cpython (gh-151436 4eab5a0?) % 

0,5% (48/9996 = 0,48%) is roughly correct, since it shouldn't be exactly linear.

I can try to come up with reproduction for each miss.

Should it be a helper?

If you ask me, the whole mechanism smells me of ABA...

• Issue: _remote_debugging: Missing last_profiled_frame updates in coroutines, generators, etc. #151436

[maurycy]

cc @pablogsal @savannahostrowski

[pablogsal]

Should it be a helper?

Yes, this should be a macro.

If you ask me, the whole mechanism smells me of ABA...

Yeah I think is still possible to have this sequence of events:

1. Profiler samples frame address A and caches stack under it.
2. Target yields/pops/removes that frame.
3. Target or allocator later has a different logical frame at address A, or the profiler races and writes stale A back after the target already moved on.
4. Profiler sees A again and says “cache hit”.
5. It reuses stale callers for a different logical stack.

we can try to think how to tackle this in a separate issue, there are some mitigations we can do

[pablogsal]

I have pushed 1348756 making this a macro

[miss-islington-app]

Thanks @maurycy for the PR, and @pablogsal for merging it 🌮🎉.. I'm working now to backport this PR to: 3.15.
🐍🍒⛏🤖

[bedevere-app]

GH-151612 is a backport of this pull request to the 3.15 branch.

[bedevere-bot]

⚠️⚠️⚠️ Buildbot failure ⚠️⚠️⚠️

Hi! The buildbot aarch64 Android 3.x (tier-3) has failed when building commit a8d74c0.

What do you need to do:

1. Don't panic.
2. Check the buildbot page in the devguide if you don't know what the buildbots are or how they work.
3. Go to the page of the buildbot that failed (https://buildbot.python.org/#/builders/1594/builds/5113) and take a look at the build logs.
4. Check if the failure is related to this commit (a8d74c0) or if it is a false positive.
5. If the failure is related to this commit, please, reflect that on the issue and make a new Pull Request with a fix.

You can take a look at the buildbot page here:

https://buildbot.python.org/#/builders/1594/builds/5113

Summary of the results of the build (if available):

Click to see traceback logs

remote: Enumerating objects: 20, done.        
remote: Counting objects:   8% (1/12)        
remote: Counting objects:  16% (2/12)        
remote: Counting objects:  25% (3/12)        
remote: Counting objects:  33% (4/12)        
remote: Counting objects:  41% (5/12)        
remote: Counting objects:  50% (6/12)        
remote: Counting objects:  58% (7/12)        
remote: Counting objects:  66% (8/12)        
remote: Counting objects:  75% (9/12)        
remote: Counting objects:  83% (10/12)        
remote: Counting objects:  91% (11/12)        
remote: Counting objects: 100% (12/12)        
remote: Counting objects: 100% (12/12), done.        
remote: Compressing objects:  16% (1/6)        
remote: Compressing objects:  33% (2/6)        
remote: Compressing objects:  50% (3/6)        
remote: Compressing objects:  66% (4/6)        
remote: Compressing objects:  83% (5/6)        
remote: Compressing objects: 100% (6/6)        
remote: Compressing objects: 100% (6/6), done.        
remote: Total 20 (delta 8), reused 6 (delta 6), pack-reused 8 (from 2)        
From https://github.com/python/cpython
 * branch                    main       -> FETCH_HEAD
Note: switching to 'a8d74c062fe3c5cb2962dde8bee83704fcfa1bc9'.

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Turn off this advice by setting config variable advice.detachedHead to false

HEAD is now at a8d74c062fe gh-151436: Fix missing `tstate->last_profiled_frame` updates (#151437)
Switched to and reset branch 'main'

configure: WARNING: no system libmpdec found; falling back to pure-Python version for the decimal module
configure: WARNING: pkg-config is missing. Some dependencies may not be detected correctly.

../../configure: line 4112: pkg-config: command not found
configure: WARNING: no system libmpdec found; falling back to pure-Python version for the decimal module
configure: WARNING: pkg-config is missing. Some dependencies may not be detected correctly.

../../Python/fileutils.c:458:1: warning: unused function 'decode_current_locale' [-Wunused-function]
  458 | decode_current_locale(const char* arg, wchar_t **wstr, size_t *wlen,
      | ^~~~~~~~~~~~~~~~~~~~~
../../Python/fileutils.c:677:1: warning: unused function 'encode_current_locale' [-Wunused-function]
  677 | encode_current_locale(const wchar_t *text, char **str,
      | ^~~~~~~~~~~~~~~~~~~~~
2 warnings generated.
../../Modules/_localemodule.c:195:1: warning: unused function 'is_all_ascii' [-Wunused-function]
  195 | is_all_ascii(const char *str)
      | ^~~~~~~~~~~~
1 warning generated.
../../Modules/pwdmodule.c:69:16: warning: unused variable 'pwd_db_mutex' [-Wunused-variable]
   69 | static PyMutex pwd_db_mutex = {0};
      |                ^~~~~~~~~~~~
1 warning generated.
../../Modules/_hacl/Lib_Memzero0.c:66:6: warning: "Your platform does not support any safe implementation of memzero -- consider a pull request!" [-W#warnings]
   66 |     #warning "Your platform does not support any safe implementation of memzero -- consider a pull request!"
      |      ^
1 warning generated.

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100  8784  100  8784    0     0  38971      0 --:--:-- --:--:-- --:--:-- 38867
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100  2894  100  2894    0     0  81003      0 --:--:-- --:--:-- --:--:-- 82685
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed

  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0
100 43504  100 43504    0     0   973k      0 --:--:-- --:--:-- --:--:--  988k
  + Exception Group Traceback (most recent call last):
  |   File "<frozen runpy>", line 198, in _run_module_as_main
  |   File "<frozen runpy>", line 88, in _run_code
  |   File "/Users/android/buildarea/3.x.mhsmith-android-aarch64/build/Platforms/Android/__main__.py", line 1059, in <module>
  |     main()
  |   File "/Users/android/buildarea/3.x.mhsmith-android-aarch64/build/Platforms/Android/__main__.py", line 1035, in main
  |     asyncio.run(result)
  |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/runners.py", line 194, in run
  |     return runner.run(main)
  |            ^^^^^^^^^^^^^^^^
  |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/runners.py", line 118, in run
  |     return self._loop.run_until_complete(task)
  |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/base_events.py", line 687, in run_until_complete
  |     return future.result()
  |            ^^^^^^^^^^^^^^^
  |   File "/Users/android/buildarea/3.x.mhsmith-android-aarch64/build/Platforms/Android/__main__.py", line 726, in run_testbed
  |     async with asyncio.TaskGroup() as tg:
  |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/taskgroups.py", line 145, in __aexit__
  |     raise me from None
  | ExceptionGroup: unhandled errors in a TaskGroup (1 sub-exception)
  +-+---------------- 1 ----------------
    | Traceback (most recent call last):
    |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/tasks.py", line 520, in wait_for
    |     return await fut
    |            ^^^^^^^^^
    |   File "/Users/android/buildarea/3.x.mhsmith-android-aarch64/build/Platforms/Android/__main__.py", line 488, in find_device
    |     await asyncio.sleep(1)
    |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/tasks.py", line 665, in sleep
    |     return await future
    |            ^^^^^^^^^^^^
    | asyncio.exceptions.CancelledError
    | 
    | The above exception was the direct cause of the following exception:
    | 
    | Traceback (most recent call last):
    |   File "/Users/android/buildarea/3.x.mhsmith-android-aarch64/build/Platforms/Android/__main__.py", line 541, in logcat_task
    |     serial = await wait_for(find_device(context, initial_devices), startup_timeout)
    |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/tasks.py", line 519, in wait_for
    |     async with timeouts.timeout(timeout):
    |   File "/Library/Frameworks/Python.framework/Versions/3.12/lib/python3.12/asyncio/timeouts.py", line 115, in __aexit__
    |     raise TimeoutError from exc_val
    | TimeoutError
    +------------------------------------