Re: [RFC PATCH 3/3] alloc_tag: remove /proc/allocinfo outside of mod_lock

On Thu, Aug 13, 2026 at 2:34 AM Hao Ge <[email protected]> wrote:
>
> shutdown_mem_profiling() calls remove_proc_entry() from
> reserve_module_tags(), which runs under mod_lock held for write.
> remove_proc_entry() waits for readers, and a reader takes mod_lock for
> read in allocinfo_start():
>
>   CPU0 (insmod)                      CPU1 (read /proc/allocinfo)
>   ----------------                   ----------------------------
>   reserve_module_tags()
>     down_write(&mod_lock)  [held]
>                                      use_pde()            [in_use++]
>                                      allocinfo_start()
>                                        down_read(&mod_lock)  <- blocks
>     shutdown_mem_profiling()
>       remove_proc_entry()
>         wait for in_use == 0         <- blocks

Yes, this is indeed a possible race.

>
> Move remove_proc_entry() to a workqueue.
>
> Fixes: 4835f747d3ed ("alloc_tag: support for page allocation tag compression")

I think all these issues were reported by Sashiko, so you should add a
Reported-by tag.

> Signed-off-by: Hao Ge <[email protected]>

LGTM

> ---
>  mm/alloc_tag.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
>
> diff --git a/mm/alloc_tag.c b/mm/alloc_tag.c
> index 7481180dadd2..b80f5a151f28 100644
> --- a/mm/alloc_tag.c
> +++ b/mm/alloc_tag.c
> @@ -591,6 +591,13 @@ void pgalloc_tag_swap(struct folio *new, struct folio *old)
>         put_page_tag_ref(handle_new);
>  }
>
> +static void remove_allocinfo_file(struct work_struct *work)
> +{
> +       remove_proc_entry(ALLOCINFO_FILE_NAME, NULL);
> +}
> +
> +static DECLARE_WORK(remove_allocinfo_work, remove_allocinfo_file);
> +
>  static void shutdown_mem_profiling(bool remove_file)
>  {
>         if (mem_alloc_profiling_enabled())
> @@ -600,7 +607,7 @@ static void shutdown_mem_profiling(bool remove_file)
>                 return;
>
>         if (remove_file)
> -               remove_proc_entry(ALLOCINFO_FILE_NAME, NULL);
> +               schedule_work(&remove_allocinfo_work);
>         mem_profiling_support = false;
>  }
>
> --
> 2.25.1
>