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 QRpZ5SNe NBCFFuK/zQIOwGl1CAicgjCgGarD7Y6qpmJTrXrwk1V7yK0uHqyHi/KYV1j7s9HR6TxCorJ8iIQkYZh3j3Pht8CugBfGk+YHRk/fDyx1WVChGQOrrp0QcNG9zT52pfSosXmZf X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 15, 2025 at 06:44:38PM +0200, Vlastimil Babka wrote: > On 10/15/25 18:29, Suren Baghdasaryan wrote: > > On Wed, Oct 15, 2025 at 7:17 AM Hao Ge wrote: > >> > >> From: Hao Ge > >> > >> If obj_exts allocation failed, slab->obj_exts is set to OBJEXTS_ALLOC_FAIL, > >> But we did 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 it was mistakenly assumed that > >> a valid folio->memcg_data was not cleared before freeing the folio. > >> > >> When freeing a slab, we clear slab->obj_exts and reset it to 0 > >> if the obj_ext array has been successfully allocated. > >> So let's reset slab->obj_exts to 0 when freeing a slab if > >> the obj_ext array allocated fail to allow them to be returned > >> to the buddy system more smoothly. > >> > >> Signed-off-by: Hao Ge > >> --- > >> v5: Adopt the simpler solution proposed by Vlastimil; > >> Many thanks to him > > I've massaged the commit log and comments a bit and also realized that > AFAICS we're actually fixing an issue that predates 7612833192d5 ("slab: > Reuse first bit for OBJEXTS_ALLOC_FAIL"). Am I wrong? You're not wrong! > ----8<---- > From 8151384e5baf34db5812ed51e2e463796ab6e973 Mon Sep 17 00:00:00 2001 > From: Hao Ge > Date: Wed, 15 Oct 2025 22:16:42 +0800 > Subject: [PATCH] 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 it was mistakenly assumed that > a valid folio->memcg_data was not cleared before freeing the folio. nit: maybe this can be massaged as "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") > Link: https://lore.kernel.org/all/20251015141642.700170-1-hao.ge@linux.dev/ > Cc: > Signed-off-by: Hao Ge > Signed-off-by: Vlastimil Babka > --- Looks good to me, Reviewed-by: Harry Yoo -- Cheers, Harry / Hyeonggon > mm/slub.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) > > 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 > -- > 2.51.0