From 8c962fb73b48d4f8fc26d3d6a30e188c323cc0b8 Mon Sep 17 00:00:00 2001
From: Andriy Svyryd <Andriy.Svyryd@microsoft.com>
Date: Thu, 7 Aug 2025 19:24:56 -0700
Subject: [PATCH] Fix race condition in RuntimeProperty.Sentinel

Fixes #36391
---
 src/EFCore/Metadata/RuntimeProperty.cs | 9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

diff --git a/src/EFCore/Metadata/RuntimeProperty.cs b/src/EFCore/Metadata/RuntimeProperty.cs
index 5efc8027355..a9e0eabd1d2 100644
--- a/src/EFCore/Metadata/RuntimeProperty.cs
+++ b/src/EFCore/Metadata/RuntimeProperty.cs
@@ -22,7 +22,7 @@ public class RuntimeProperty : RuntimePropertyBase, IRuntimeProperty
     private readonly ValueGenerated _valueGenerated;
     private readonly bool _isConcurrencyToken;
     private object? _sentinel;
-    private object? _sentinelFromProviderValue;
+    private volatile object? _sentinelFromProviderValue;
     private readonly PropertySaveBehavior _beforeSaveBehavior;
     private readonly PropertySaveBehavior _afterSaveBehavior;
     private readonly Func<IProperty, ITypeBase, ValueGenerator>? _valueGeneratorFactory;
@@ -335,11 +335,12 @@ public override object? Sentinel
     {
         get
         {
-            if (_sentinelFromProviderValue != null)
+            var providerValue = _sentinelFromProviderValue;
+            if (providerValue != null)
             {
-                var providerValue = _sentinelFromProviderValue;
+                Interlocked.CompareExchange(ref _sentinel, TypeMapping.Converter!.ConvertFromProvider(providerValue), null);
+
                 _sentinelFromProviderValue = null;
-                _sentinel = TypeMapping.Converter!.ConvertFromProvider(providerValue);
             }
 
             return _sentinel;