Fix context pooling concurrency issue

Fixes #26202

(cherry picked from commit 8e09d65)

src/EFCore/DbContext.cs

@@ -822,11 +822,17 @@ public virtual void Dispose()
             }
         }
 
+        /// <summary>
+        ///     Releases the allocated resources for this context.
+        /// </summary>
+        public virtual ValueTask DisposeAsync()
+            => DisposeSync() ? _serviceScope.DisposeAsyncIfAvailable() : default;
+
         private bool DisposeSync()
         {
             if (_lease.IsActive)
             {
-                if (_lease.ContextDisposed())
+                if (_lease.IsStandalone)
                 {
                     _disposed = true;
 
@@ -835,7 +841,10 @@ private bool DisposeSync()
                         ClearEvents();
                     }
 
+                    var lease = _lease;
                     _lease = DbContextLease.InactiveLease;
+
+                    lease.ContextDisposed();
                 }
             }
             else if (!_disposed)
@@ -863,13 +872,6 @@ private bool DisposeSync()
             return false;
         }
 
-        /// <summary>
-        ///     Releases the allocated resources for this context.
-        /// </summary>
-        public virtual ValueTask DisposeAsync()
-            => DisposeSync() ? _serviceScope.DisposeAsyncIfAvailable() : default;
-
-
         private static readonly bool _dontClearEvents
             = AppContext.TryGetSwitch("Microsoft.EntityFrameworkCore.Issue23108", out var isEnabled) && isEnabled;
 

src/EFCore/Internal/DbContextLease.cs

@@ -15,7 +15,14 @@ namespace Microsoft.EntityFrameworkCore.Internal
     public struct DbContextLease
     {
         private IDbContextPool _contextPool;
-        private readonly bool _standalone;
+
+        /// <summary>
+        ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
+        ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
+        ///     any release. You should only use it directly in your code with extreme caution and knowing that
+        ///     doing so can result in application failures when updating to a new Entity Framework Core release.
+        /// </summary>
+        public bool IsStandalone { get; }
 
         /// <summary>
         ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
@@ -34,7 +41,7 @@ public struct DbContextLease
         public DbContextLease([NotNull] IDbContextPool contextPool, bool standalone)
         {
             _contextPool = contextPool;
-            _standalone = standalone;
+            IsStandalone = standalone;
 
             var context = _contextPool.Rent();
             Context = context;
@@ -65,16 +72,12 @@ public bool IsActive
         ///     any release. You should only use it directly in your code with extreme caution and knowing that
         ///     doing so can result in application failures when updating to a new Entity Framework Core release.
         /// </summary>
-        public bool ContextDisposed()
+        public void ContextDisposed()
         {
-            if (_standalone)
+            if (IsStandalone)
             {
                 Release();
-
-                return true;
             }
-
-            return false;
         }
 
         /// <summary>

test/EFCore.SqlServer.FunctionalTests/DbContextPoolingTest.cs

@@ -1264,6 +1264,33 @@ private async Task WriteResults()
             }
         }
 
+        [ConditionalTheory]
+        [InlineData(false)]
+        [InlineData(true)]
+        public async Task Concurrency_test2(bool async)
+        {
+            var factory = BuildServiceProviderWithFactory<PooledContext>()
+                .GetService<IDbContextFactory<PooledContext>>();
+
+            await Task.WhenAll(
+                Enumerable.Range(0, 10).Select(_ => Task.Run(async () =>
+                {
+                    for (var j = 0; j < 1_000_000; j++)
+                    {
+                        var ctx = factory.CreateDbContext();
+
+                        if (async)
+                        {
+                            await ctx.DisposeAsync();
+                        }
+                        else
+                        {
+                            ctx.Dispose();
+                        }
+                    }
+                })));
+        }
+
         private async Task Dispose(IDisposable disposable, bool async)
         {
             if (async)