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b=V19wazKLOp6RZkUtSjNDmzHzKEfwQSNjcp6NByfAVngPZ0F6yzYVlqqkdelSC2hhG 3QTantQ+D9kN69D1kwsFw1Wv6WID3xWN0+FMRT47gVBUUxqcpjBKhkbDotL7CWGf4z X+hgMNOwVcULaAja0DyLZI2q/w1HT/Ch6ZePWc1QO3SVlCCj1qCJKtXJuAquvmTFjA bD46Ggr+9OlrrRCk9dPF/JGcdBtsK8mvUES3FnHa+6u2Pj/Y2TXtuT9TK2pQAP67Pj bhoQrJAC9ebDHtFNz2dAN3FkGZzbRdAP8YwbLU2Q8mKMvFhcZZVZ2PwgUmpmvvl/nO kkQeyh+iGv7qw== Message-ID: Date: Wed, 29 Jul 2026 11:46:11 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 06/13] mm/slab: abstract slabobj_ext.ref access Content-Language: en-US To: Harry Yoo Cc: Suren Baghdasaryan , Hao Li , Shakeel Butt , Alexander Potapenko , Marco Elver , Andrew Morton , Christoph Lameter , David Rientjes , Roman Gushchin , linux-mm@kvack.org, linux-kernel@vger.kernel.org, cgroups@vger.kernel.org References: <20260727-b4-objext_split-v3-0-c29ef0f1f257@kernel.org> <20260727-b4-objext_split-v3-6-c29ef0f1f257@kernel.org> <365d8e50-5aeb-45e9-97a3-87d0024cdc5f@kernel.org> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 3B03580011 X-Rspam-User: X-Stat-Signature: s9kcaw6wx9ipug4wykwqxoe6d9hq6yb9 X-HE-Tag: 1785318376-478226 X-HE-Meta: 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 dRxjiMDo 8pGvY+z9W3rTUgUVCXvDkKt/ULSAG96vFvhkjilghzKZoIwYayztb0UJbp/utll3zHHYG0RVeC8UVRapv8rtMKe+A06c7nPNejT7FCoTifp2F2DpiTxobBjguRzU7nlmgTl2E6OUeX16CJ7NW7TaM9YqgVsk8dIXxcs/FRR0Xm7czNvNbguUUUtxpAodJ4nacwbJSaBsD56QZ59o+B01LbOCSa8nukzGnCbMRq8iTxUOyPr0lW1s3iKtVeuzYSbakWAc/hrxSxspFm6I95Ej5Dja1oGcEVexj3/kDYP0W12uPnvbzftIiSILZPCTvHKML8YkP68UlGM3KpcAKgUwxQSseDuHq6Wt1BeWbSyOsSNX2DOSrtHbzTnWzD1sN/l56eJTtTjxkIE8SKKZR2mdYi+3O/S3b+Jg02YzZUQnBKf3pGVlOHP/S2oVEhw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 7/29/26 08:18, Harry Yoo wrote: >> diff --git a/mm/slab.h b/mm/slab.h >> index 8f352d9f4d91..fbad99da093c 100644 >> --- a/mm/slab.h >> +++ b/mm/slab.h >> @@ -726,6 +726,8 @@ static inline void slab_obj_ext_set_objcg(struct slabobj_ext *obj_ext, >> static inline union codetag_ref * >> slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext) >> { >> + VM_WARN_ON_ONCE(!slab_obj_ext_has_codetag()); >> + >> if (IS_ENABLED(CONFIG_MEMCG)) >> obj_ext += 1; >> >> ... and for objcg we would need to start passing slab pointer to >> slab_obj_ext_objcg() and slab_obj_ext_set_objcg(). Hmm... > > But slab_obj_ext_codetag_ref() already takes the parameter to > calculate offset. I think it's worth as it'll be optimized away on > non-debug kerenels and there is no way to detect type confusion > due to subtle errors in the objext layout. OK, so updated to this. VM_WARN_ON_ONCE() added later. >From db9c3501c0f9747fda8fa92d4f640b6fac8050e0 Mon Sep 17 00:00:00 2001 From: "Vlastimil Babka (SUSE)" Date: Mon, 27 Jul 2026 14:53:59 +0200 Subject: [PATCH] mm/slab: abstract slabobj_ext.objcg access In preparation for changes to the structure, abstract getting and setting the objcg field with slab_obj_ext_objcg() and slab_obj_ext_set_objcg(). Rename the field to _objcg to make an unexpected direct access a compile error. The helpers take a slab pointer, which is currently unused, but will be used by a debug check later. Since there is no slab pointer easily available in __kfence_free(), just drop the debug check there. The whole memcg_kmem accounting in kfence is to be removed later anyway. Otherwise, no functional change intended. Reviewed-by: Hao Li Reviewed-by: Suren Baghdasaryan Reviewed-by: Harry Yoo (Oracle) Link: https://patch.msgid.link/20260727-b4-objext_split-v3-5-c29ef0f1f257@kernel.org Signed-off-by: Vlastimil Babka (SUSE) --- mm/kfence/core.c | 3 --- mm/memcontrol.c | 14 ++++++++------ mm/slab.h | 17 ++++++++++++++++- mm/slub.c | 2 +- 4 files changed, 25 insertions(+), 11 deletions(-) diff --git a/mm/kfence/core.c b/mm/kfence/core.c index 6577bd76954e..5608a37f2b4d 100644 --- a/mm/kfence/core.c +++ b/mm/kfence/core.c @@ -1248,9 +1248,6 @@ void __kfence_free(void *addr) { struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr); -#ifdef CONFIG_MEMCG - KFENCE_WARN_ON(meta->obj_exts.objcg); -#endif /* * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing * the object, as the object page may be recycled for other-typed diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 4e427286a88a..68e98fb3350e 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -2865,6 +2865,7 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) */ unsigned long obj_exts; struct slabobj_ext *obj_ext; + struct obj_cgroup *objcg; obj_exts = slab_obj_exts(slab); if (!obj_exts) @@ -2872,9 +2873,8 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p) get_slab_obj_exts(obj_exts); obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p); - if (obj_ext->objcg) { - struct obj_cgroup *objcg = obj_ext->objcg; - + objcg = slab_obj_ext_objcg(slab, obj_ext); + if (objcg) { put_slab_obj_exts(obj_exts); return obj_cgroup_memcg(objcg); } @@ -3614,8 +3614,10 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru, obj_exts = slab_obj_exts(slab); get_slab_obj_exts(obj_exts); obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]); + obj_cgroup_get(objcg); - obj_ext->objcg = objcg; + slab_obj_ext_set_objcg(slab, obj_ext, objcg); + put_slab_obj_exts(obj_exts); } @@ -3633,11 +3635,11 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab, struct obj_stock_pcp *stock; obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]); - objcg = obj_ext->objcg; + objcg = slab_obj_ext_objcg(slab, obj_ext); if (!objcg) continue; - obj_ext->objcg = NULL; + slab_obj_ext_set_objcg(slab, obj_ext, NULL); stock = trylock_stock(); __refill_obj_stock(objcg, stock, obj_size, true); diff --git a/mm/slab.h b/mm/slab.h index 451b50b7f237..ea014311e29f 100644 --- a/mm/slab.h +++ b/mm/slab.h @@ -555,7 +555,7 @@ static inline bool need_kmalloc_no_objext(void) */ struct slabobj_ext { #ifdef CONFIG_MEMCG - struct obj_cgroup *objcg; + struct obj_cgroup *_objcg; #endif #ifdef CONFIG_MEM_ALLOC_PROFILING union codetag_ref ref; @@ -662,6 +662,21 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts, return kasan_reset_tag(obj_ext); } +#ifdef CONFIG_MEMCG +static inline struct obj_cgroup * +slab_obj_ext_objcg(struct slab *slab, struct slabobj_ext *obj_ext) +{ + return obj_ext->_objcg; +} + +static inline void +slab_obj_ext_set_objcg(struct slab *slab, struct slabobj_ext *obj_ext, + struct obj_cgroup *objcg) +{ + obj_ext->_objcg = objcg; +} +#endif + int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s, gfp_t gfp, unsigned int alloc_flags); diff --git a/mm/slub.c b/mm/slub.c index a74f1866c958..ed18860fa0fd 100644 --- a/mm/slub.c +++ b/mm/slub.c @@ -2526,7 +2526,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags) if (obj_exts) { get_slab_obj_exts(obj_exts); obj_ext = slab_obj_ext(s, slab, obj_exts, p); - if (unlikely(obj_ext->objcg)) { + if (unlikely(slab_obj_ext_objcg(slab, obj_ext))) { put_slab_obj_exts(obj_exts); return true; } -- 2.55.0