[PATCH] mm/page_alloc: clear page tag refs when onlining hotplugged memory

[Zenghui Yu <zenghui.yu@linux.dev>]

From: "Zenghui Yu (Huawei)" <zenghui.yu@linux.dev>

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

Onlined pages enter the buddy allocator without ever being allocated, so
their allocation tag references are NULL.  The free path expects a valid
tag or a CODETAG_EMPTY mark and warns otherwise.  Other paths feeding
never-allocated pages into the buddy (memblock_free_pages(),
init_cma_reserved_pageblock(), free_reserved_pages()) mark them with
clear_page_tag_ref() first; the hotplug onlining path was missed.

Mark the pages as not tagged in the MEMINIT_HOTPLUG branch of
__free_pages_core(), where PageOffline and the refcount are already
reset.

Signed-off-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
---
 mm/page_alloc.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index e71e514ea18d..9561f2cd873e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1604,6 +1604,7 @@ void __meminit __free_pages_core(struct page *page, unsigned int order,
 			VM_WARN_ON_ONCE(PageReserved(p));
 			__ClearPageOffline(p);
 			set_page_count(p, 0);
+			clear_page_tag_ref(p);
 		}
 
 		adjust_managed_page_count(page, nr_pages);
-- 
2.56.0