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[3.14] gh-148820: Fix _PyRawMutex use-after-free on spurious semaphore wakeup (gh-148852) - #148884
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…maphore wakeup (pythongh-148852) _PyRawMutex_UnlockSlow CAS-removes the waiter from the list and then calls _PySemaphore_Wakeup, with no handshake. If _PySemaphore_Wait returns Py_PARK_INTR, the waiter can destroy its stack-allocated semaphore before the unlocker's Wakeup runs, causing a fatal error from ReleaseSemaphore / sem_post. Loop in _PyRawMutex_LockSlow until _PySemaphore_Wait returns Py_PARK_OK, which is only signalled when a matching Wakeup has been observed. Also include GetLastError() and the handle in the Windows fatal messages in _PySemaphore_Init, _PySemaphore_Wait, and _PySemaphore_Wakeup to make similar races easier to diagnose in the future. (cherry picked from commit ad3c5b7) Co-authored-by: Sam Gross <colesbury@gmail.com>
This was referenced Apr 22, 2026
colesbury
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April 22, 2026 18:48
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_PyRawMutex_UnlockSlow CAS-removes the waiter from the list and then calls _PySemaphore_Wakeup, with no handshake. If _PySemaphore_Wait returns Py_PARK_INTR, the waiter can destroy its stack-allocated semaphore before the unlocker's Wakeup runs, causing a fatal error from ReleaseSemaphore / sem_post.
Loop in _PyRawMutex_LockSlow until _PySemaphore_Wait returns Py_PARK_OK, which is only signalled when a matching Wakeup has been observed.
Also include GetLastError() and the handle in the Windows fatal messages in _PySemaphore_Init, _PySemaphore_Wait, and _PySemaphore_Wakeup to make similar races easier to diagnose in the future.
(cherry picked from commit ad3c5b7)