Re: [External] Re: [PATCH 1/3] mm/slub: Fix slabs_node return value when CONFIG_SLUB_DEBUG disabled

[Muchun Song <songmuchun@bytedance.com>]

On Mon, Jun 15, 2020 at 2:11 PM Joonsoo Kim <js1304@gmail.com> wrote:
>
> 2020년 6월 14일 (일) 오후 9:39, Muchun Song <songmuchun@bytedance.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@bytedance.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