Re: [PATCH v2] mm/codetag: clear tags before swap

[Suren Baghdasaryan <surenb@google.com>]

On Thu, Dec 12, 2024 at 12:29 AM David Wang <00107082@163.com> wrote:
>
> When CONFIG_MEM_ALLOC_PROFILING_DEBUG is set, kernel WARN would be
> triggered when calling __alloc_tag_ref_set() during swap:
>
>         alloc_tag was not cleared (got tag for mm/filemap.c:1951)
>         WARNING: CPU: 0 PID: 816 at ./include/linux/alloc_tag.h...
>
> Clear code tags before swap can fix the warning. And this patch also fix
> a potential invalid address dereference in alloc_tag_add_check() when
> CONFIG_MEM_ALLOC_PROFILING_DEBUG is set and ref->ct is CODETAG_EMPTY,
> which is defined as ((void *)1).
>
> Signed-off-by: David Wang <00107082@163.com>
> Reported-by: kernel test robot <oliver.sang@intel.com>
> Closes: https://lore.kernel.org/oe-lkp/202412112227.df61ebb-lkp@intel.com
> Suggested-by: Suren Baghdasaryan <surenb@google.com>

I didn't really suggest much in this patch, so please replace above
Suggested-by with:

Acked-by: Suren Baghdasaryan <surenb@google.com>

Thanks for fixing this!

> ---
>  include/linux/alloc_tag.h | 2 +-
>  lib/alloc_tag.c           | 7 +++++++
>  2 files changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/include/linux/alloc_tag.h b/include/linux/alloc_tag.h
> index 7c0786bdf9af..cba024bf2db3 100644
> --- a/include/linux/alloc_tag.h
> +++ b/include/linux/alloc_tag.h
> @@ -135,7 +135,7 @@ static inline struct alloc_tag_counters alloc_tag_read(struct alloc_tag *tag)
>  #ifdef CONFIG_MEM_ALLOC_PROFILING_DEBUG
>  static inline void alloc_tag_add_check(union codetag_ref *ref, struct alloc_tag *tag)
>  {
> -       WARN_ONCE(ref && ref->ct,
> +       WARN_ONCE(ref && ref->ct && !is_codetag_empty(ref),
>                   "alloc_tag was not cleared (got tag for %s:%u)\n",
>                   ref->ct->filename, ref->ct->lineno);
>
> diff --git a/lib/alloc_tag.c b/lib/alloc_tag.c
> index 35f7560a309a..3a0413462e9f 100644
> --- a/lib/alloc_tag.c
> +++ b/lib/alloc_tag.c
> @@ -209,6 +209,13 @@ void pgalloc_tag_swap(struct folio *new, struct folio *old)
>                 return;
>         }
>
> +       /*
> +        * Clear tag references to avoid debug warning when using
> +        * __alloc_tag_ref_set() with non-empty reference.
> +        */
> +       set_codetag_empty(&ref_old);
> +       set_codetag_empty(&ref_new);
> +
>         /* swap tags */
>         __alloc_tag_ref_set(&ref_old, tag_new);
>         update_page_tag_ref(handle_old, &ref_old);
> --
> 2.39.2
>