Avoid a race condition in opt-viewer/optrecord #131214
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See https://bugzilla.redhat.com/2336915 See https://reviews.llvm.org/D41784?id= See androm3da/optviewer-demo#4 (comment) Fixes llvm#62403 The race condition happened when the demangler_proc was being set. The locking mechanism itself happened too late. This way, the lock always exists (to avoid a race when creating it) and is always used when *creating* demangler_proc. I don't have any prior experience with the codebase and I cannot guarantee the behavior is correct. It appears to get rid of the race (which I was seeing consistently). multiprocessing.pool.RemoteTraceback: """ Traceback (most recent call last): File "/usr/lib64/python3.14/multiprocessing/pool.py", line 125, in worker result = (True, func(*args, **kwds)) ~~~~^^^^^^^^^^^^^^^ File "/usr/lib64/python3.14/multiprocessing/pool.py", line 48, in mapstar return list(map(*args)) File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/optpmap.py", line 25, in _wrapped_func return func(argument, filter_) File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/opt-viewer.py", line 293, in _render_file SourceFileRenderer(source_dir, output_dir, filename, no_highlight).render(remarks) ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^ File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/opt-viewer.py", line 216, in render self.render_source_lines(self.source_stream, line_remarks) ~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/opt-viewer.py", line 123, in render_source_lines self.render_inline_remarks(remark, html_line) ~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^ File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/opt-viewer.py", line 126, in render_inline_remarks inlining_context = r.DemangledFunctionName ^^^^^^^^^^^^^^^^^^^^^^^ File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/optrecord.py", line 153, in DemangledFunctionName return self.demangle(self.Function) ~~~~~~~~~~~~~^^^^^^^^^^^^^^^ File "/builddir/build/BUILD/llvm-19.1.6-build/llvm-project-19.1.6.src/llvm/tools/opt-viewer/optrecord.py", line 77, in demangle with cls.demangler_lock: ^^^^^^^^^^^^^^^^^^ AttributeError: type object 'Passed' has no attribute 'demangler_lock'. Did you mean: 'demangler_proc'? """
| @@ -64,17 +64,19 @@ class Remark(yaml.YAMLObject): | |||
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| default_demangler = "c++filt -n" | |||
| demangler_proc = None | |||
| demangler_lock = Lock() | |||
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I 100% agree with that.
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| @classmethod | ||
| def demangle(cls, name): | ||
| with cls.demangler_lock: | ||
| if not cls.demangler_proc: |
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does this really need to be within the Lock?
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So the underlying problem is that before that patch, caller had to ensure set_demangler was called before calling demangle.
A neater way to enforce that would be to make demangler_proc lazily initialized, but the proposed approach is fine as demangler_proc is only referenced from demangle
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When it's outside of the lock, two workers could attempt to create the process.
- worker A sees demangler_proc is None
- worker B sees demangler_proc is None
- worked A assigns a new process to demangler_proc
- worker B assigns a new process to demangler_proc
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I was even getting stuff like:
File "/builddir/build/BUILD/llvm-20.1.0-build/llvm-project-20.1.0.src/llvm/tools/opt-viewer/optrecord.py", line 160, in DemangledFunctionName
return self.demangle(self.Function)
~~~~~~~~~~~~~^^^^^^^^^^^^^^^
File "/builddir/build/BUILD/llvm-20.1.0-build/llvm-project-20.1.0.src/llvm/tools/opt-viewer/optrecord.py", line 85, in demangle
cls.demangler_proc.stdin.write((name + "\n").encode("utf-8"))
^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'NoneType' object has no attribute 'stdin'
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/cherry-pick e0f8898 |
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LLVM Buildbot has detected a new failure on builder Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/19363 Here is the relevant piece of the build log for the reference |
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/pull-request #134058 |
See https://bugzilla.redhat.com/2336915 See https://reviews.llvm.org/D41784?id= See androm3da/optviewer-demo#4 (comment) Fixes llvm#62403. The race condition happened when the demangler_proc was being set. The locking mechanism itself happened too late. This way, the lock always exists (to avoid a race when creating it) and is always used when *creating* demangler_proc. (cherry picked from commit e0f8898)
See https://bugzilla.redhat.com/2336915
See https://reviews.llvm.org/D41784?id=
See androm3da/optviewer-demo#4 (comment)
Fixes #62403
The race condition happened when the demangler_proc was being set. The locking mechanism itself happened too late.
This way, the lock always exists (to avoid a race when creating it) and is always used when creating demangler_proc.
I don't have any prior experience with the codebase and I cannot guarantee the behavior is correct.
It appears to get rid of the race (which I was seeing consistently).