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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142

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Merged

[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
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davidwrighton:backport/pr-129021-to-release/10.0

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Backport of #129021 to release/10.0

Fixes#128401

/cc @leculver

Customer Impact

  • Customer reported
  • Found internally

This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.

Regression

  • Yes
  • No

This was introduced in #113943

Testing

Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.

Risk

  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.

Risks:
This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.

IMPORTANT: If this backport is for a servicing release, please verify that:

  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).

Package authoring no longer needed in .NET 9

IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.
Keep in mind that we still need package authoring in .NET 8 and older versions.

CopilotAI review requested due to automatic review settings June 8, 2026 23:01
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Pull request overview

Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.

Changes:

  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.

Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.

Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton changed the title Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton changed the title Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT added the Servicing-approved Approved for servicing release label Jun 15, 2026
@JulieLeeMSFTJulieLeeMSFT added this to the 10.0.x milestone Jun 15, 2026
@JulieLeeMSFT
JulieLeeMSFT merged commit eca7096 into dotnet:release/10.0Jun 15, 2026
110 of 113 checks passed
@dotnet-maestrodotnet-maestroBot mentioned this pull request Jun 15, 2026
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@davidwrightondavidwrighton mentioned this pull request Jun 22, 2026
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
Skip to content
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
Merged
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Jun 15, 2026
Merged
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
CopilotAI
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June 8, 2026 23:01
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT
added
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Jun 15, 2026
@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Jun 15, 2026
@JulieLeeMSFT
JulieLeeMSFT
merged commit eca7096
into
dotnet:release/10.0Jun 15, 2026

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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
Skip to content
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
Merged
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Jun 15, 2026
Merged
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Conversation
@davidwrighton
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Jun 8, 2026

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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
CopilotAI
review requested due to automatic review settings
June 8, 2026 23:01
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT
added
the 
Servicing-approved
Approved for servicing release
label
Jun 15, 2026
@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Jun 15, 2026
@JulieLeeMSFT
JulieLeeMSFT
merged commit eca7096
into
dotnet:release/10.0Jun 15, 2026

110 of 113 checks passed

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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
Skip to content
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
Merged
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Jun 15, 2026
Merged
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
CopilotAI
review requested due to automatic review settings
June 8, 2026 23:01
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
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Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
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, 'i');
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
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// Try immediately
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lastUrl = location.href;
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observer.observe(document.body, { childList: true, subtree: true });
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
Skip to content
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
Merged
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Jun 15, 2026
Merged
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
CopilotAI
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT
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@JulieLeeMSFTJulieLeeMSFT
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@JulieLeeMSFT
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})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
Skip to content
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
Merged
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
Jun 15, 2026
Merged
[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
JulieLeeMSFT merged 8 commits into
dotnet:release/10.0from 
davidwrighton:backport/pr-129021-to-release/10.0
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
CopilotAI
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
changed the title
Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@JulieLeeMSFTJulieLeeMSFT
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Jun 15, 2026
@JulieLeeMSFTJulieLeeMSFT
added this to the 10.0.x milestone
Jun 15, 2026
@JulieLeeMSFT
JulieLeeMSFT
merged commit eca7096
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dotnet:release/10.0Jun 15, 2026

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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst by davidwrighton · Pull Request #129142 · dotnet/runtime · GitHub
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst - #129142
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[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crst#129142
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Backport of #129021 to release/10.0
Fixes#128401
/cc @leculver
Customer Impact
  •  Customer reported
  •  Found internally
This was reported by customers which found that a service in production would deadlock occasionally when perfmap generation was enabled.
Regression
  •  Yes
  •  No
This was introduced in #113943
Testing
Fix was verified through analysis, and the fix also includes an escape hatch environment variable (DOTNET_PerfMapGranularity=4) which will disable the problematic code entirely.
Risk
  1. This fix is only applicable to customers which use perfmaps
  2. The fix not only includes code changes which fix the deadlock problem from happening, but also includes a change to add a config switch to avoid the problematic code entirely while keeping the perfmap generation for most scenarios which are interesting to customers.
Risks:

This fix adjusts a lock so that it will not switch to preemptive mode, and we will run some file I/O while under that lock. This may cause GC latency spikes on some customer workloads. This issue is mitigated by the new switch which can be used to avoid the problem in its entirety at the cost of slightly less accurate profile data for a limited set of scenarios.
IMPORTANT: If this backport is for a servicing release, please verify that:
  • For .NET 8 and .NET 9: The PR target branch is release/X.0-staging, not release/X.0.
  • For .NET 10+: The PR target branch is release/X.0 (no -staging suffix).
Package authoring no longer needed in .NET 9
IMPORTANT: Starting with .NET 9, you no longer need to edit a NuGet package's csproj to enable building and bump the version.

Keep in mind that we still need package authoring in .NET 8 and older versions.
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June 8, 2026 23:01
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Pull request overview
Backport of the .NET 10 CoreCLR PerfMap deadlock fix to release/10.0, addressing a lock-ordering / GC-mode-toggle deadlock when PerfMap stub logging runs on paths that hold CRST_UNSAFE_ANYMODE locks (notably virtual-call-stub / code fragment heap allocation paths). The change also introduces a configuration escape hatch to disable stub logging while keeping PerfMap generation available for other symbol types.
Changes:
  • Make the PerfMap lock (PerfMap::s_csPerfMap) CRST_UNSAFE_ANYMODE to prevent cooperative↔preemptive GC-mode toggling while under other UNSAFE_ANYMODE locks.
  • Add a PerfMapStubGranularity bit to disable stub logging (value 4), providing an escape hatch for affected customers.
  • Adjust virtual call stub generation paths to optionally switch GC mode around stub generation and to reinitialize bucket-table probers after potential GC-mode transitions.
Reviewed changes
Copilot reviewed 5 out of 5 changed files in this pull request and generated 3 comments.
Show a summary per file
FileDescription
src/coreclr/vm/virtualcallstub.cppWraps stub generation with conditional GC-mode switching when PerfMap is enabled, and refreshes probers after potential invalidation; removes FEATURE_PERFMAP guards around stub logging calls.
src/coreclr/vm/perfmap.hAdds a no-FEATURE_PERFMAP stub PerfMap definition and introduces s_LogStubs in the FEATURE_PERFMAP path.
src/coreclr/vm/perfmap.cppSwitches PerfMap crst to CRST_UNSAFE_ANYMODE, adds s_LogStubs config handling, and gates stub logging on the new switch.
src/coreclr/vm/eventing/eventpipe/ds-rt-coreclr.hUpdates PerfMap enable path contracts for diagnostics-server activation.
src/coreclr/inc/clrconfigvalues.hUpdates the PerfMapStubGranularity description to document the new “disable stub logging” bit.
Comment threadsrc/coreclr/vm/perfmap.h
Comment threadsrc/coreclr/vm/virtualcallstub.cpp
Comment threadsrc/coreclr/inc/clrconfigvalues.h
@davidwrightondavidwrighton
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Backport/pr 129021 to release/10.0Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
@davidwrightondavidwrighton
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Backport/pr 129021 to release/10.0 : Change the PerfMap crst into an UNSAFE_ANYMODE crst[release/10.0] : Change the PerfMap crst into an UNSAFE_ANYMODE crstJun 10, 2026
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Jun 15, 2026
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