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Date: Mon, 15 Jun 2020 15:11:06 +0900 From: Joonsoo Kim <js1304@...il.com> To: Muchun Song <songmuchun@...edance.com> Cc: Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Linux Memory Management List <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org> Subject: Re: [PATCH 1/3] mm/slub: Fix slabs_node return value when CONFIG_SLUB_DEBUG disabled 2020년 6월 14일 (일) 오후 9:39, Muchun Song <songmuchun@...edance.com>님이 작성: > > The slabs_node() always return zero when CONFIG_SLUB_DEBUG is disabled. > But some codes determine whether slab is empty by checking the return > value of slabs_node(). As you know, the result is not correct. This > problem can be reproduce by the follow code(and boot system with the > cmdline of "slub_nomerge"): > > void *objs[32]; > struct kmem_cache *cache = kmem_cache_create("kmem-test", 128, 0, > 0, 0); > > if (cache) { > int i; > > /* Make a full slab */ > for (i = 0; i < ARRAY_SIZE(objs); i++) > objs[i] = kmem_cache_alloc(cache, GFP_KERNEL_ACCOUNT); > > /* > * This really should fail because the slab cache still has > * objects. But we did destroy the @cache because of zero > * returned by slabs_node(). > */ > kmem_cache_destroy(cache); > } > > To fix it, we can move the nr_slabs of kmem_cache_node out of the > CONFIG_SLUB_DEBUG. So we can get the corrent value returned by the > slabs_node(). > > With this patch applied, we will get a warning message and stack > trace in the dmesg. > > Signed-off-by: Muchun Song <songmuchun@...edance.com> > --- > mm/slab.h | 2 +- > mm/slub.c | 80 +++++++++++++++++++++++++++++++++------------------------------ > 2 files changed, 43 insertions(+), 39 deletions(-) > > diff --git a/mm/slab.h b/mm/slab.h > index 0b91f2a7b033..062d4542b7e2 100644 > --- a/mm/slab.h > +++ b/mm/slab.h > @@ -619,8 +619,8 @@ struct kmem_cache_node { > #ifdef CONFIG_SLUB > unsigned long nr_partial; > struct list_head partial; > -#ifdef CONFIG_SLUB_DEBUG > atomic_long_t nr_slabs; > +#ifdef CONFIG_SLUB_DEBUG > atomic_long_t total_objects; > struct list_head full; > #endif > diff --git a/mm/slub.c b/mm/slub.c > index 49b5cb7da318..1a3e6a5b7287 100644 > --- a/mm/slub.c > +++ b/mm/slub.c Hello, You also need to initialize nr_slabs in init_kmem_cache_node() on !CONFIG_SLUB_DEBUG. Otherwise, looks good to me. Thanks.
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