linux-kernel - Re: [uClinux-dev] v3.15-rc1 slab allocator broken on m68knommu (coldfire)

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Date:	Thu, 17 Apr 2014 12:09:43 -0700
From:	Steven King <sfking@...dc.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [uClinux-dev] v3.15-rc1 slab allocator broken on m68knommu (coldfire)

On Wednesday 16 April 2014 6:49:11 pm Joonsoo Kim wrote:
> On Wed, Apr 16, 2014 at 10:44:11AM -0700, Steven King wrote:
> > On Wednesday 16 April 2014 9:06:57 am Geert Uytterhoeven wrote:
> > > Hi Steven,
> > >
> > > On Wed, Apr 16, 2014 at 5:47 PM, Steven King <sfking@...dc.com> wrote:
> > > > --- a/mm/slab.c
> > > > +++ b/mm/slab.c
> > > > @@ -2572,13 +2572,13 @@ static void *alloc_slabmgmt(struct kmem_cache
> > > > *cachep, return freelist;
> > > >  }
> > > >
> > > > -static inline freelist_idx_t get_free_obj(struct page *page,
> > > > unsigned char idx) +static inline freelist_idx_t get_free_obj(struct
> > > > page *page, unsigned int idx) {
> > > >         return ((freelist_idx_t *)page->freelist)[idx];
> > > >  }
> > > >
> > > >  static inline void set_free_obj(struct page *page,
> > > > -                                       unsigned char idx,
> > > > freelist_idx_t val) +                                       unsigned
> > > > int idx, freelist_idx_t val) {
> > > >         ((freelist_idx_t *)(page->freelist))[idx] = val;
> > > >  }
> > > >
> > > >
> > > > then v3.15-rc1 will boot using the slab allocator.
> > >
> > > Is "idx" ever larger than 255?
> > >
> > > Gr{oetje,eeting}s,
> >
> > Yes.  If I stick
> >
> >         if (idx > 255)
> >                 pr_info("%s %d\n", __func__, idx);
> >
> > in get_free_obj and set_free_obj and see values for idx up into the 400s.
>
> Hello,
>
> Yes, it's my mistake. idx can be larger than 255 if freelist_idx_t is
> unsigned short. So unsigned char idx isn't appropriate here. Your
> system's PAGE_SIZE may be 2^13, so freelist_idx_t would be unsigned short
> and idx will be larger than 255.
>
> Your fix looks good to me, so could you send it quickly to Pekka with
> some description? If you don't have enough time to do it, I can handle it.
>
> Really thanks for notifying this issue.
>
> Thanks.

Why don't you go ahead and do it, you know whats going better than I do.
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