linux-kernel - Re: [PATCH v3 32/35] codetag: debug: skip objext checking when it's for objext itself

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Date: Mon, 19 Feb 2024 08:55:22 -0800
From: Suren Baghdasaryan <surenb@...gle.com>
To: Vlastimil Babka <vbabka@...e.cz>
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Subject: Re: [PATCH v3 32/35] codetag: debug: skip objext checking when it's
 for objext itself

On Mon, Feb 19, 2024 at 1:17 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>
> On 2/19/24 02:04, Suren Baghdasaryan wrote:
> > On Fri, Feb 16, 2024 at 6:39 PM Vlastimil Babka <vbabka@...e.cz> wrote:
> >>
> >> On 2/12/24 22:39, Suren Baghdasaryan wrote:
> >> > objext objects are created with __GFP_NO_OBJ_EXT flag and therefore have
> >> > no corresponding objext themselves (otherwise we would get an infinite
> >> > recursion). When freeing these objects their codetag will be empty and
> >> > when CONFIG_MEM_ALLOC_PROFILING_DEBUG is enabled this will lead to false
> >> > warnings. Introduce CODETAG_EMPTY special codetag value to mark
> >> > allocations which intentionally lack codetag to avoid these warnings.
> >> > Set objext codetags to CODETAG_EMPTY before freeing to indicate that
> >> > the codetag is expected to be empty.
> >> >
> >> > Signed-off-by: Suren Baghdasaryan <surenb@...gle.com>
> >> > ---
> >> >  include/linux/alloc_tag.h | 26 ++++++++++++++++++++++++++
> >> >  mm/slab.h                 | 25 +++++++++++++++++++++++++
> >> >  mm/slab_common.c          |  1 +
> >> >  mm/slub.c                 |  8 ++++++++
> >> >  4 files changed, 60 insertions(+)
> >> >
> >> > diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> >> > index 0a5973c4ad77..1f3207097b03 100644
> >>
> >> ...
> >>
> >> > index c4bd0d5348cb..cf332a839bf4 100644
> >> > --- a/mm/slab.h
> >> > +++ b/mm/slab.h
> >> > @@ -567,6 +567,31 @@ static inline struct slabobj_ext *slab_obj_exts(struct slab *slab)
> >> >  int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> >> >                       gfp_t gfp, bool new_slab);
> >> >
> >> > +
> >> > +#ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
> >> > +
> >> > +static inline void mark_objexts_empty(struct slabobj_ext *obj_exts)
> >> > +{
> >> > +     struct slabobj_ext *slab_exts;
> >> > +     struct slab *obj_exts_slab;
> >> > +
> >> > +     obj_exts_slab = virt_to_slab(obj_exts);
> >> > +     slab_exts = slab_obj_exts(obj_exts_slab);
> >> > +     if (slab_exts) {
> >> > +             unsigned int offs = obj_to_index(obj_exts_slab->slab_cache,
> >> > +                                              obj_exts_slab, obj_exts);
> >> > +             /* codetag should be NULL */
> >> > +             WARN_ON(slab_exts[offs].ref.ct);
> >> > +             set_codetag_empty(&slab_exts[offs].ref);
> >> > +     }
> >> > +}
> >> > +
> >> > +#else /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
> >> > +
> >> > +static inline void mark_objexts_empty(struct slabobj_ext *obj_exts) {}
> >> > +
> >> > +#endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
> >> > +
> >>
> >> I assume with alloc_slab_obj_exts() moved to slub.c, mark_objexts_empty()
> >> could move there too.
> >
> > No, I think mark_objexts_empty() belongs here. This patch introduced
> > the function and uses it. Makes sense to me to keep it all together.
>
> Hi,
>
> here I didn't mean moving between patches, but files. alloc_slab_obj_exts()
> in slub.c means all callers of mark_objexts_empty() are in slub.c so it
> doesn't need to be in slab.h

Ah, I see. I misunderstood your comment. Yes, after slab/slob cleanup
this makes sense.

>
> Also same thing with mark_failed_objexts_alloc() and
> handle_failed_objexts_alloc() in patch 34/35.

Ack. Thanks!

>