From 1cdac61065e72db60d26e03ef9286d2743d7000e Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Thu, 21 Oct 2021 08:39:58 -0700
Subject: bpo-45521: Fix a bug in the obmalloc radix tree code. (GH-29051)
 (GH-29122)

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.
(cherry picked from commit 311910b31a4bd94dc79298388b7cb65ca5546438)
---
 .../next/Core and Builtins/2021-10-18-22-40-33.bpo-45521.GdMiuW.rst    | 3 +++
 Objects/obmalloc.c                                                     | 2 +-
 2 files changed, 4 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Core and Builtins/2021-10-18-22-40-33.bpo-45521.GdMiuW.rst

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
new file mode 100644
index 0000000..3a082a4
--- /dev/null
+++ 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
index 15c442b..615703a 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -1328,7 +1328,7 @@ _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)
-- 
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