Port, board and/or hardware

unix port, standard variant, x86_64, debian trixie

MicroPython version

MicroPython v1.27.0-preview.388.g27544a2d81 on 2025-11-13; linux [GCC 14.2.0] version

Reproduction

$ make -C ports/unix
$ ports/unix/build-standard/micropython -X emit=native tests/thread/stress_schedule.py

Expected behaviour

Expected to print "PASS"

Observed behaviour

After about 10 seconds prints "4", meaning that only 4 scheduled tasks ran during the test. This happens consistently.

Additional Information

It works when "-X emit=native" is omitted.

On the "good" side of the bisect it sometimes fails but prints a large number like 9158, meaning it almost succeeded. The "bad" side always prints 4.

I don't understand why it's not seen during CI; perhaps debian trixie has some detail of threading different than ubuntu 24.04, or perhaps my computer's configuration is different in a relevant way (12 thread Intel i5-1235U)

I attempted to diagnose this further and bisected it to (ping @projectgus)

52a593cdb14ed732b5580bbed39c0325815adedf is the first bad commit
commit 52a593cdb14ed732b5580bbed39c0325815adedf
Author: Angus Gratton <angus@redyak.com.au>
Date:   Wed Sep 4 17:17:38 2024 +1000

    py/scheduler: Only run callbacks on the main thread if GIL is disabled.
    
    Otherwise it's very difficult to reason about thread safety in a
    scheduler callback, as it can run at any time on any thread - including
    racing against any bytecode operation on any thread.
    
    This work was funded through GitHub Sponsors.
    
    Signed-off-by: Angus Gratton <angus@redyak.com.au>

 docs/library/micropython.rst | 8 ++++++++
 py/scheduler.c               | 8 +++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

<details>
<summary>git bisect log</summary>

(micropython) jepler@bert:~/src/micropython/ports/unix$ git bisect log
git bisect start
# status: waiting for both good and bad commits
# good: [8cd15829e293f01dae91b6a2d4a995bfaeca887b] all: Bump version to 1.22.2.
git bisect good 8cd15829e293f01dae91b6a2d4a995bfaeca887b
# status: waiting for bad commit, 1 good commit known
# bad: [b15348415e9d5ad2a978ca38a8da356faee88e91] extmod/modframebuf: Add support for blit'ing read-only data.
git bisect bad b15348415e9d5ad2a978ca38a8da356faee88e91
# good: [9feb0689eeaca5ce88aedcc680f997a3b4d0221c] all: Bump version to 1.22.0.
git bisect good 9feb0689eeaca5ce88aedcc680f997a3b4d0221c
# bad: [e5eeaa7df894b5062c189f5d8da44c67550cf43a] docs/reference/mpremote: Update docs to mention new features.
git bisect bad e5eeaa7df894b5062c189f5d8da44c67550cf43a
# good: [03cf4d4980af604ebae6928f51a311b53d98e2c8] rp2/boards/W5500_EVB_PICO: Update incorrect url in board.json.
git bisect good 03cf4d4980af604ebae6928f51a311b53d98e2c8
# good: [052693e4495354daabb4d61e97121283334c6665] esp32/boards: Reduce IRAM usage.
git bisect good 052693e4495354daabb4d61e97121283334c6665
# good: [3294606e2319dd64226434f20acc15b8869ddf55] extmod/libmetal: Fix libmetal rules for mkdir dependencies.
git bisect good 3294606e2319dd64226434f20acc15b8869ddf55
# bad: [eec5eb4260ebc76694f751f0966f4c8236da9609] stm32/uart: Add UART RX/CTS pin pull config options.
git bisect bad eec5eb4260ebc76694f751f0966f4c8236da9609
# good: [ded8bbdd5efc50d2b86e3020462ced8bbcf4d25c] rp2/machine_pin_cyw43: Include check for CYW43_GPIO.
git bisect good ded8bbdd5efc50d2b86e3020462ced8bbcf4d25c
# bad: [d775db72b9bf01d2f40f6cf4d4d98941f30b7bd2] esp32/boards/UM_FEATHERS3NEO: Add FeatherS3 Neo board definition.
git bisect bad d775db72b9bf01d2f40f6cf4d4d98941f30b7bd2
# bad: [7b5738ad86f11eef682c5a649754777d2935a156] tools/ci.sh: Clean up the Unix port's MIPS target.
git bisect bad 7b5738ad86f11eef682c5a649754777d2935a156
# bad: [5d8878b582b8b68d19ab02adfe32d683d5ea512f] shared/tinyusb: Only run TinyUSB on the main thread if GIL is disabled.
git bisect bad 5d8878b582b8b68d19ab02adfe32d683d5ea512f
# bad: [52a593cdb14ed732b5580bbed39c0325815adedf] py/scheduler: Only run callbacks on the main thread if GIL is disabled.
git bisect bad 52a593cdb14ed732b5580bbed39c0325815adedf
# good: [451ba1cf386a2a0874ea20ea593dd6a009ede011] rp2/modules: Fix FatFS boot script to detect invalid FAT filesystem.
git bisect good 451ba1cf386a2a0874ea20ea593dd6a009ede011
# first bad commit: [52a593cdb14ed732b5580bbed39c0325815adedf] py/scheduler: Only run callbacks on the main thread if GIL is disabled.

</summary>

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