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

[Suren Baghdasaryan <surenb@google.com>]

On Fri, Feb 16, 2024 at 6:39 PM Vlastimil Babka <vbabka@suse.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@google.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.

>
> >  static inline bool need_slab_obj_ext(void)
> >  {
> >  #ifdef CONFIG_MEM_ALLOC_PROFILING
> > diff --git a/mm/slab_common.c b/mm/slab_common.c
> > index 21b0b9e9cd9e..d5f75d04ced2 100644
> > --- a/mm/slab_common.c
> > +++ b/mm/slab_common.c
> > @@ -242,6 +242,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
> >                * assign slabobj_exts in parallel. In this case the existing
> >                * objcg vector should be reused.
> >                */
> > +             mark_objexts_empty(vec);
> >               kfree(vec);
> >               return 0;
> >       }
> > diff --git a/mm/slub.c b/mm/slub.c
> > index 4d480784942e..1136ff18b4fe 100644
> > --- a/mm/slub.c
> > +++ b/mm/slub.c
> > @@ -1890,6 +1890,14 @@ static inline void free_slab_obj_exts(struct slab *slab)
> >       if (!obj_exts)
> >               return;
> >
> > +     /*
> > +      * obj_exts was created with __GFP_NO_OBJ_EXT flag, therefore its
> > +      * corresponding extension will be NULL. alloc_tag_sub() will throw a
> > +      * warning if slab has extensions but the extension of an object is
> > +      * NULL, therefore replace NULL with CODETAG_EMPTY to indicate that
> > +      * the extension for obj_exts is expected to be NULL.
> > +      */
> > +     mark_objexts_empty(obj_exts);
> >       kfree(obj_exts);
> >       slab->obj_exts = 0;
> >  }
>