From: Hao Ge Date: Wed, 15 Oct 2025 14:16:42 +0000 (+0800) Subject: slab: reset slab->obj_ext when freeing and it is OBJEXTS_ALLOC_FAIL X-Git-Url: https://www.infradead.org/git/?a=commitdiff_plain;h=86f54f9b6c17d6567c69e3a6fed52fdf5d7dbe93;p=users%2Fhch%2Fmisc.git slab: reset slab->obj_ext when freeing and it is OBJEXTS_ALLOC_FAIL If obj_exts allocation failed, slab->obj_exts is set to OBJEXTS_ALLOC_FAIL, But we do not clear it when freeing the slab. Since OBJEXTS_ALLOC_FAIL and MEMCG_DATA_OBJEXTS currently share the same bit position, during the release of the associated folio, a VM_BUG_ON_FOLIO() check in folio_memcg_kmem() is triggered because the OBJEXTS_ALLOC_FAIL flag was not cleared, causing it to be interpreted as a kmem folio (non-slab) with MEMCG_OBJEXTS_DATA flag set, which is invalid because MEMCG_OBJEXTS_DATA is supposed to be set only on slabs. Another problem that predates sharing the OBJEXTS_ALLOC_FAIL and MEMCG_DATA_OBJEXTS bits is that on configurations with is_check_pages_enabled(), the non-cleared bit in page->memcg_data will trigger a free_page_is_bad() failure "page still charged to cgroup" When freeing a slab, we clear slab->obj_exts if the obj_ext array has been successfully allocated. So let's clear it also when the allocation has failed. Fixes: 09c46563ff6d ("codetag: debug: introduce OBJEXTS_ALLOC_FAIL to mark failed slab_ext allocations") Fixes: 7612833192d5 ("slab: Reuse first bit for OBJEXTS_ALLOC_FAIL") Link: https://lore.kernel.org/all/20251015141642.700170-1-hao.ge@linux.dev/ Cc: Signed-off-by: Hao Ge Reviewed-by: Suren Baghdasaryan Reviewed-by: Harry Yoo Signed-off-by: Vlastimil Babka --- diff --git a/mm/slub.c b/mm/slub.c index 13ae4491136a..a8fcc7e6f25a 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2170,8 +2170,15 @@ static inline void free_slab_obj_exts(struct slab *slab) struct slabobj_ext *obj_exts; obj_exts = slab_obj_exts(slab); - if (!obj_exts) + if (!obj_exts) { + /* + * If obj_exts allocation failed, slab->obj_exts is set to + * OBJEXTS_ALLOC_FAIL. In this case, we end up here and should + * clear the flag. + */ + slab->obj_exts = 0; return; + } /* * obj_exts was created with __GFP_NO_OBJ_EXT flag, therefore its