One-time-use allocated blocks keep reference to source pool / Assert that a block is returned to it's source pool / Managed block are only returned to active Slabs

Author: clrjunkie

src/Microsoft.AspNet.Server.Kestrel/Infrastructure/MemoryPool2.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Concurrent;
+using System.Diagnostics;
 
 namespace Microsoft.AspNet.Server.Kestrel.Infrastructure
 {
@@ -76,7 +77,7 @@ public MemoryPoolBlock2 Lease(int minimumSize = MaxPooledBlockLength)
                 return MemoryPoolBlock2.Create(
                     new ArraySegment<byte>(new byte[minimumSize]),
                     dataPtr: IntPtr.Zero,
-                    pool: null,
+                    pool: this,
                     slab: null);
             }
 
@@ -137,11 +138,13 @@ private MemoryPoolBlock2 AllocateSlab()
         /// <param name="block">The block to return. It must have been acquired by calling Lease on the same memory pool instance.</param>
         public void Return(MemoryPoolBlock2 block)
         {
-            if (block.Slab != null)
+            Debug.Assert(block.Pool == this, "Returned block was leased from this pool");
+
+            if (block.Slab != null && block.Slab.IsActive)
             {
                 block.Reset();
                 _blocks.Enqueue(block);
-            }
+            }            
         }
 
         protected virtual void Dispose(bool disposing)