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Date: Mon, 15 Jun 2020 14:26:16 +0800 From: Muchun Song <songmuchun@...edance.com> To: Joonsoo Kim <js1304@...il.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: [External] Re: [PATCH 1/3] mm/slub: Fix slabs_node return value when CONFIG_SLUB_DEBUG disabled On Mon, Jun 15, 2020 at 2:11 PM Joonsoo Kim <js1304@...il.com> wrote: > > 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. Good catch, thanks! I will fix it in the next version. > > Otherwise, looks good to me. > > Thanks. -- Yours, Muchun
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