From b6732c6d43139ea56de8bc62e87ace8543ef784f Mon Sep 17 00:00:00 2001 From: "Zenghui Yu (Huawei)" Date: Thu, 22 Oct 2026 20:27:52 +0800 Subject: [PATCH] mm/page_alloc: mark pages freed by __free_pages_core() as not tagged Onlining hotplugged memory (e.g., a dev_dax device bound to kmem) with CONFIG_MEM_ALLOC_PROFILING_DEBUG triggers: alloc_tag was not set WARNING: ./include/linux/alloc_tag.h:166 at __pgalloc_tag_sub+0x1fc/0x254 Call trace: __pgalloc_tag_sub+0x1fc/0x254 (P) __free_pages_ok+0x14c/0x6ac __free_pages_core+0xa8/0x188 generic_online_page+0x14/0x20 online_pages+0x220/0x3b0 memory_subsys_online+0xfc/0x198 device_online+0x58/0xe0 state_store+0xf0/0xf8 Pages entering the buddy through __free_pages_core() have never been allocated, so their allocation tag references are NULL. The free path, __free_pages_prepare() -> pgalloc_tag_sub(), expects a valid tag or a CODETAG_EMPTY mark and warns otherwise. Paths feeding never-allocated pages into the buddy are therefore expected to mark them with clear_page_tag_ref() first, like init_cma_reserved_pageblock() and free_reserved_pages() do; of __free_pages_core()'s callers only memblock_free_pages() clears the tag ref itself, and the hotplug onlining path was missed. Since all __free_pages_core() callers free never-allocated pages, mark the head page as not tagged in __free_pages_core() itself instead of relying on each caller, and drop the now-redundant clearing from memblock_free_pages(). Link: https://lore.kernel.org/20261022122752.74774-1-zenghui.yu@linux.dev Fixes: dcfe378c81f7 ("lib: introduce support for page allocation tagging") Signed-off-by: Zenghui Yu (Huawei) Signed-off-by: Andrew Morton Reviewed-by: Johannes Weiner Cc: Mike Rapoport Cc: Vlastimil Babka Cc: Suren Baghdasaryan Cc: Michal Hocko Cc: Brendan Jackman Cc: Zi Yan Cc: --- mm/mm_init.c | 2 -- mm/page_alloc.c | 3 +++ 2 files changed, 3 insertions(+), 2 deletions(-) diff --git a/mm/mm_init.c b/mm/mm_init.c index 2a0e782a151d..d99af80ec752 100644 --- a/mm/mm_init.c +++ b/mm/mm_init.c @@ -2478,8 +2478,6 @@ void __init memblock_free_pages(unsigned long pfn, unsigned int order) return; } - /* pages were reserved and not allocated */ - clear_page_tag_ref(page); __free_pages_core(page, order, MEMINIT_EARLY); } diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 31ba24411d36..2b2855300217 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -1616,6 +1616,9 @@ void __meminit __free_pages_core(struct page *page, unsigned int order, atomic_long_add(nr_pages, &page_zone(page)->managed_pages); } + /* pages were never allocated */ + clear_page_tag_ref(page); + if (page_contains_unaccepted(page, order)) { if (order == MAX_PAGE_ORDER && __free_unaccepted(page)) return;