From 867cf402792bfc3b6db01c800cbce0e59fb3cfe1 Mon Sep 17 00:00:00 2001
From: "Miss Islington (bot)"
 <31488909+miss-islington@users.noreply.github.com>
Date: Wed, 10 Jul 2024 19:05:11 +0200
Subject: [3.13] gh-121460: Skip freeing unallocated arenas (gh-121589)

`munmap(NULL)` is not noop, like `free(NULL)` is.

Fixes an observed testsuite hang on 32-bit ARM systems.

(cherry picked from commit a802277914405786f6425f2776605c44bd407fc0, AKA gh-121491)

Co-authored-by: Stefano Rivera <stefano@rivera.za.net>
---
 Objects/obmalloc.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/Objects/obmalloc.c b/Objects/obmalloc.c
index 4fe195b..a9decc5 100644
--- a/Objects/obmalloc.c
+++ b/Objects/obmalloc.c
@@ -386,8 +386,16 @@ _PyMem_ArenaFree(void *Py_UNUSED(ctx), void *ptr,
 )
 {
 #ifdef MS_WINDOWS
+    /* Unlike free(), VirtualFree() does not special-case NULL to noop. */
+    if (ptr == NULL) {
+        return;
+    }
     VirtualFree(ptr, 0, MEM_RELEASE);
 #elif defined(ARENAS_USE_MMAP)
+    /* Unlike free(), munmap() does not special-case NULL to noop. */
+    if (ptr == NULL) {
+        return;
+    }
     munmap(ptr, size);
 #else
     free(ptr);
-- 
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