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[3.14] gh-137400: Fix a crash when disabling profiling across all threads (gh-137471) #137648

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[3.14] gh-137400: Fix a crash when disabling profiling across all threads (gh-137471) #137648

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@miss-islington miss-islington commented Aug 11, 2025 •
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The PyEval_SetProfileAllThreads function and other related functions
had a race condition on tstate->c_profilefunc that could lead to a
crash when disable profiling or tracing on all threads while another
thread is starting to profile or trace a a call.

There are still potential crashes when threads exit concurrently with
profiling or tracing be enabled/disabled across all threads.
(cherry picked from commit 3626928)

Co-authored-by: Sam Gross colesbury@gmail.com

@colesbury @miss-islington
pythongh-137400: Fix a crash when disabling profiling across all thre…
77f9ca6 
…ads (pythongh-137471)

The `PyEval_SetProfileAllThreads` function and other related functions
had a race condition on `tstate->c_profilefunc` that could lead to a
crash when disable profiling or tracing on all threads while another
thread is starting to profile or trace a a call.

There are still potential crashes when threads exit concurrently with
profiling or tracing be enabled/disabled across all threads.
(cherry picked from commit 3626928)

Co-authored-by: Sam Gross <colesbury@gmail.com>
This was referenced Aug 11, 2025
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@hugovk

From @pablogsal's comment in #137400 (comment):

The worry we have is that this is going to segfault for a bunch of users, and we’ll burn a lot of effort trying to diagnose whether issues are caused by this bug or something else.

So it would be great to get it in 3.14.0 if possible, but we understand if that’s not possible or if you want to wait until the next release.

From our perspective, having users hit segfaults in production when using memray with Python 3.14.0 has the risk to create a significant support burden - we’d have to triage every crash report to determine if it’s this known issue or something new and given the nature of this problem that may be a pain to guide the user or even get a reproducer. Getting the fix into 3.14.0 would save both our users and ourselves from that pain.

That said, we appreciate the trade-offs involved here so if the bigger fix needs more time to bake, the smaller fix in 3.14.0 might be a reasonable compromise to at least prevent the segfaults, even if it doesn’t address all the thread-safety issues.​​​​​​​​​​​​​​​​

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@colesbury colesbury colesbury approved these changes

@kumaraditya303 kumaraditya303 kumaraditya303 approved these changes

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