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

Suren Baghdasaryan
2024-02-19T01:05:08Z

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;
> > }
>