From ef66779d0b927df73d63d027750e6b6907271a38 Mon Sep 17 00:00:00 2001
From: Stefano Rivera <stefano@rivera.za.net>
Date: Wed, 10 Jul 2024 09:40:55 -0700
Subject: [PATCH] gh-121460: Skip freeing unallocated arenas (gh-121491)

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

Fixes an observed testsuite hang on 32-bit ARM systems.
(cherry picked from commit a802277914405786f6425f2776605c44bd407fc0)

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 4fe195b63166c1..a9decc5dc1b1dd 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);