Avoid populating shared patch bypass buffer after initial creation#117514
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tommcdon merged 9 commits intodotnet:mainfrom Jul 16, 2025
Merged
Avoid populating shared patch bypass buffer after initial creation#117514tommcdon merged 9 commits intodotnet:mainfrom
tommcdon merged 9 commits intodotnet:mainfrom
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Pull Request Overview
This PR refactors how the shared patch bypass buffer is created and accessed to eliminate a race condition by making the buffer read-only once it exists.
- Split
GetOrCreateSharedPatchBypassBufferinto separateCreateSharedPatchBypassBufferandGetSharedPatchBypassBuffermethods - Updated
DebuggerPatchSkipto only write to the buffer on initial creation and skip writes thereafter - Renamed calls and added guards around RW versus RX buffer access
Reviewed Changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.
| File | Description |
|---|---|
| src/coreclr/debug/ee/controller.h | Renamed buffer accessor, splitting creation and retrieval into two distinct methods |
| src/coreclr/debug/ee/controller.cpp | Changed patch-skip logic to only populate the buffer when first created and guard subsequent writes |
Comments suppressed due to low confidence (2)
src/coreclr/debug/ee/controller.h:554
- [nitpick] The comment is now misleading for
CreateSharedPatchBypassBuffer. Consider updating it to describe that this method always creates a new buffer rather than just retrieving one.
// gets a pointer to the shared buffer
src/coreclr/debug/ee/controller.cpp:4534
- The variable name
SharedPatchBypassBufferWriterHolderhere refers to the class, not the instance. It should besharedPatchBypassBufferWriterHolder.AssignExecutableWriterHolder(...)to match the declared variable.
SharedPatchBypassBufferWriterHolder.AssignExecutableWriterHolder((SharedPatchBypassBuffer*)m_pSharedPatchBypassBuffer, sizeof(SharedPatchBypassBuffer));
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This was referenced Jul 10, 2025
noahfalk
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Jul 11, 2025
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A few more style/refactoring suggestions inline. LGTM!
Co-authored-by: Noah Falk <[email protected]>
Encapsulate instruction attribute into SharedBypasBuffer
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Android timeout is unrelated, merging |
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/ba-g failures are unrelated |
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Fixes #102767
This pull request changes DebuggerPatchSkip creation. Before this change we always populated the shared patch bypass buffer, which is used for patch skipping. Although the population of the patch skip buffer is done under the DebuggerController lock, as it is a shared buffer, it's possible we write to it while other threads are executing in the patch buffer which runs without the DebuggerController lock. This exposes a small race condition that can be hit with multiple threads executing on the same breakpoint location. This fix addresses the issue by effectively making the buffer read-only after it is created. There was a previous comment in the code stating that we always overwrite the buffer due to ReJIT jump stamps. Jump stamps were removed in the .NET Core 2.2 timeframe, and so it is believed that it should be safe to avoid constantly re-writing the patch buffer for each DebuggerPatchSkip creation