bpo-45521: Fix a bug in the obmalloc radix tree code. (GH-29051)

nascheme · web-flow · commit 311910b31a4b · 2021-10-21T06:38:36.000-07:00
MAP_BOT_LENGTH was incorrectly used to compute MAP_TOP_MASK instead of
MAP_TOP_LENGTH. On 64-bit machines, the error causes the tree to hold
46-bits of virtual addresses, rather than the intended 48-bits.
diff --git a/Misc/NEWS.d/next/Core and Builtins/2021-10-18-22-40-33.bpo-45521.GdMiuW.rst b/Misc/NEWS.d/next/Core and Builtins/2021-10-18-22-40-33.bpo-45521.GdMiuW.rst
@@ -0,0 +1,3 @@
+Fix a bug in the obmalloc radix tree code.  On 64-bit machines, the bug
+causes the tree to hold 46-bits of virtual addresses, rather than the
+intended 48-bits.
diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
@@ -1341,7 +1341,7 @@ _Py_GetAllocatedBlocks(void)
 
 #define MAP_TOP_BITS INTERIOR_BITS
 #define MAP_TOP_LENGTH (1 << MAP_TOP_BITS)
-#define MAP_TOP_MASK (MAP_BOT_LENGTH - 1)
+#define MAP_TOP_MASK (MAP_TOP_LENGTH - 1)
 
 #define MAP_MID_BITS INTERIOR_BITS
 #define MAP_MID_LENGTH (1 << MAP_MID_BITS)

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,3 @@`
	`1`	`+Fix a bug in the obmalloc radix tree code. On 64-bit machines, the bug`
	`2`	`+causes the tree to hold 46-bits of virtual addresses, rather than the`
	`3`	`+intended 48-bits.`