From a100fe7e873bc6311f09fdcf1dc42225524827cf Mon Sep 17 00:00:00 2001 From: devdavidejesus Date: Sat, 24 Oct 2026 08:37:37 -0300 Subject: [PATCH] gh-160588: Restore the gh-123022 check in the vendored mimalloc The mimalloc 2.5.2 update dropped the check that skips _mi_heap_random_next() while the thread's default heap is not initialized. Without it, Py_Initialize() in a background thread crashes on free-threaded release builds of 3.14. --- Objects/mimalloc/os.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/Objects/mimalloc/os.c b/Objects/mimalloc/os.c index ab1813a74724417..b6e2ecbbd080e2d 100644 --- a/Objects/mimalloc/os.c +++ b/Objects/mimalloc/os.c @@ -126,8 +126,12 @@ void* _mi_os_get_aligned_hint(size_t try_alignment, size_t size) if (hint == 0 || hint > MI_HINT_MAX) { // wrap or initialize uintptr_t init = MI_HINT_BASE; #if (MI_SECURE>0 || MI_DEBUG==0) // security: randomize start of aligned allocations unless in debug mode - uintptr_t r = _mi_heap_random_next(mi_prim_get_default_heap()); - init = init + ((MI_SEGMENT_SIZE * ((r>>17) & 0xFFFFF)) % MI_HINT_AREA); // (randomly 20 bits)*4MiB == 0 to 4TiB + mi_heap_t* heap = mi_prim_get_default_heap(); + // gh-123022: default heap may not be initialized in CPython in background threads + if (mi_heap_is_initialized(heap)) { + uintptr_t r = _mi_heap_random_next(heap); + init = init + ((MI_SEGMENT_SIZE * ((r>>17) & 0xFFFFF)) % MI_HINT_AREA); // (randomly 20 bits)*4MiB == 0 to 4TiB + } #endif uintptr_t expected = hint + size; mi_atomic_cas_strong_acq_rel(&aligned_base, &expected, init); @@ -636,8 +640,12 @@ static uint8_t* mi_os_claim_huge_pages(size_t pages, size_t* total_size) { // Initialize the start address after the 32TiB area start = ((uintptr_t)32 << 40); // 32TiB virtual start address #if (MI_SECURE>0 || MI_DEBUG==0) // security: randomize start of huge pages unless in debug mode - uintptr_t r = _mi_heap_random_next(mi_prim_get_default_heap()); - start = start + ((uintptr_t)MI_HUGE_OS_PAGE_SIZE * ((r>>17) & 0x0FFF)); // (randomly 12bits)*1GiB == between 0 to 4TiB + mi_heap_t* heap = mi_prim_get_default_heap(); + // gh-123022: default heap may not be initialized in CPython in background threads + if (mi_heap_is_initialized(heap)) { + uintptr_t r = _mi_heap_random_next(heap); + start = start + ((uintptr_t)MI_HUGE_OS_PAGE_SIZE * ((r>>17) & 0x0FFF)); // (randomly 12bits)*1GiB == between 0 to 4TiB + } #endif } end = start + size;