Fix bug with freeing page which wasn't allocated

Also add more assertions to fsm.c.

Author: Alexander Korotkov

contrib/in_memory/fdw_descr.c

@@ -211,7 +211,7 @@ imFetchDescrForOidWithShared(Oid oid, SharedDescr *shared_descr)
 	}
 	PG_CATCH();
 	{
-		for (i = 0; i <= MaxIndices; i++)
+		for (i = 0; i < MaxIndices; i++)
 		{
 			if (PageNumberIsValid(shared_descr->tree[i].root))
 				fsm_free_page(shared_descr->tree[i].root);

contrib/in_memory/fsm.c

@@ -122,7 +122,7 @@ init_fsm(Pointer ptr, bool found)
 	}
 
 	/* Initialize non-leafs */
-	for (i = 0; i < fsm_non_leaf; i++)
+	for (i = 0; i < FSM_BRANCH_FACTOR; i++)
 		init_fsm_non_leaf_recursive(i);
 }
 
@@ -142,6 +142,7 @@ fsm_get_page(void)
 
 		for (j = i; j < i + FSM_BRANCH_FACTOR; j++)
 		{
+			Assert(j >= 0 && j < fsm_non_leaf);
 			uint32	val = pg_atomic_read_u32(&fsm[j]);
 			if (val != 0)
 			{
@@ -170,10 +171,13 @@ fsm_get_page(void)
 		{
 			uint32	val = pg_atomic_read_u32(&fsm[j]);
 
+			Assert(j >= fsm_non_leaf && j < fsm_total);
+
 			if (val != 0xFFFFFFFF)
 			{
-				int		bitno = 0;
-				uint32	bit = (val + 1) & ~val;
+				PageNumber	result;
+				int			bitno = 0;
+				uint32		bit = (val + 1) & ~val;
 
 				val = pg_atomic_fetch_or_u32(&fsm[j], bit);
 				if ((val & bit) != 0)
@@ -182,7 +186,9 @@ fsm_get_page(void)
 				bit >>= 1;
 				while (bit > 0) { bitno++; bit >>= 1; }
 				Assert(bitno < 32);
-				return (j - fsm_non_leaf) * 32 + bitno;
+				result = (j - fsm_non_leaf) * 32 + bitno;
+				Assert(result <= shared_pool_size / IN_MEMORY_BLCKSZ);
+				return result;
 			}
 		}
 	}
@@ -211,12 +217,15 @@ fsm_free_page(PageNumber pageno)
 	i = pageno / 32 + fsm_non_leaf;
 	bitno = pageno % 32;
 
+	Assert(i >= fsm_non_leaf && i < fsm_total);
+
 	Assert((pg_atomic_read_u32(&fsm[i]) & (1 << bitno)) != 0);
 	pg_atomic_fetch_and_u32(&fsm[i], ~(1 << bitno));
 
 	while (i >= FSM_BRANCH_FACTOR)
 	{
 		i = (i / FSM_BRANCH_FACTOR) - 1;
+		Assert(i >= 0 && i < fsm_non_leaf);
 		pg_atomic_fetch_add_u32(&fsm[i], 1);
 	}
 }