[Release/3.1] Fixes for profiler stack sampling (#27300)

* only set THREAD_IS_SUSPENDED if we are truly doing an async stack walk (#26985)

* Use a new COR_PRF_SUSPEND_FOR_PROFILER in ICorProfilerCallback::RuntimeThreadSuspended() when requested by profiler (#27041)

Fixes https://github.com/dotnet/coreclr/issues/26576

2 files changed, 17 insertions, 3 deletions

diff --git a/src/vm/proftoeeinterfaceimpl.cpp b/src/vm/proftoeeinterfaceimpl.cpp
index cff17213a7..e0caccf4a2 100644
--- a/src/vm/proftoeeinterfaceimpl.cpp
+++ b/src/vm/proftoeeinterfaceimpl.cpp
@@ -8285,15 +8285,27 @@ HRESULT ProfToEEInterfaceImpl::DoStackSnapshot(ThreadID thread,
         // with destructors.
         AVInRuntimeImplOkayHolder AVOkay;
 
+        DWORD asyncFlags = 0;
+        if (pThreadToSnapshot != pCurrentThread)
+        {
+            asyncFlags |= ALLOW_ASYNC_STACK_WALK;
+            if (!g_profControlBlock.fProfilerRequestedRuntimeSuspend)
+            {
+                // THREAD_IS_SUSPENDED signals to the stack walker that the
+                // thread is interrupted at an arbitrary point and to be careful
+                // not to cause a deadlock. If the profiler suspended the runtime,
+                // then we know the threads are at a safe place and we can walk all the threads.
+                asyncFlags |= THREAD_IS_SUSPENDED;
+            }
+        }
+
         hr = DoStackSnapshotHelper(
                  pThreadToSnapshot, 
                  &data, 
                  HANDLESKIPPEDFRAMES |
                      FUNCTIONSONLY |
                      NOTIFY_ON_U2M_TRANSITIONS |
-                     ((pThreadToSnapshot == pCurrentThread) ?
-                         0 : 
-                         ALLOW_ASYNC_STACK_WALK | THREAD_IS_SUSPENDED) |
+                     asyncFlags |
                      THREAD_EXECUTING_MANAGED_CODE |
                      PROFILER_DO_STACK_SNAPSHOT |
                      ALLOW_INVALID_OBJECTS, // stack walk logic should not look at objects - we could be in the middle of a gc.
diff --git a/src/vm/threadsuspend.cpp b/src/vm/threadsuspend.cpp
index 9c0af1f913..a47812ba7d 100644
--- a/src/vm/threadsuspend.cpp
+++ b/src/vm/threadsuspend.cpp
@@ -3762,6 +3762,8 @@ COR_PRF_SUSPEND_REASON GCSuspendReasonToProfSuspendReason(ThreadSuspend::SUSPEND
         return COR_PRF_SUSPEND_FOR_INPROC_DEBUGGER;
     case ThreadSuspend::SUSPEND_FOR_GC_PREP:
         return COR_PRF_SUSPEND_FOR_GC_PREP;
+    case ThreadSuspend::SUSPEND_FOR_PROFILER:
+        return COR_PRF_SUSPEND_FOR_PROFILER;
     }
 }
 #endif // PROFILING_SUPPORTED