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

Vlastimil Babka
2024-02-16T18:39:58Z

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.

> 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;
> }