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gh-129185: Fix PyTraceMalloc_Untrack() at Python exit #129191
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gh-129185: Fix PyTraceMalloc_Untrack() at Python exit
vstinner 4172b91
Test also PyTraceMalloc_Untrack() without the GIL
vstinner f3ec095
Call _PyTraceMalloc_Fini() after finalize_interp_clear()
vstinner d510567
PyTraceMalloc_Track() checks tracing with the GIL
vstinner 31bfe5b
Test also Untrack in test_tracemalloc_track_race()
vstinner 555c70d
Get the GIL in Untrack
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We need to hold the lock or GIL, right?
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The purpose of this "pre-check" is to avoid the GIL and TABLES_LOCK().
The flag is tested again below with TABLES_LOCK().
PyTraceMalloc_Untrack() doesn't lock the GIL, only TABLES_LOCK(), when tracing.
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This change restores the check that we had before recent refactoring. For example, Python 3.14 alpha3 uses:
The check is done without holding the GIL.
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But then we lose the thread safety: if one thread that holds the GIL were to write to
tracing
, then a thread that calls one of these without the GIL would race.There was a problem hiding this comment.
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I think the easiest solution would be to grab the tables lock for the read, and then unlock it before calling
PyGILState_Ensure
to prevent lock-ordering deadlocks.There was a problem hiding this comment.
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What is the problem of "continue execution" of thread A, since thread A checks again
tracing
with the tables lock?There was a problem hiding this comment.
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Because it might not reach the second
tracing
read at all--if the first one races, then we're probably going to get a crash.There was a problem hiding this comment.
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Ah, you're talking about thread B calling
_PyTraceMalloc_Fini()
, nottracemalloc.stop()
. In this case, thread A can callTABLES_LOCK()
after thread B deleted the lock, and yes, we can get a crash.Sadly, PyTraceMalloc_Track() and PyTraceMalloc_Untrack() API doesn't require the caller to hold the GIL.
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That can happen too, but I meant that we'll get a crash from the data race on
tracing
, not a use-after-free on the lock. I think we just hold the GIL (viaPyGILState_Ensure
) and call without the tables lock held, that should be thread safe enough for 3.12.There was a problem hiding this comment.
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I modified the Untrack() function to get the GIL. It should address your last concern.