Re: [PATCH v2 4/4] kasan: use stack_trace_save_shadow

[Marco Elver <elver@google.com>]

On Wed, 23 Mar 2022 at 16:33, <andrey.konovalov@linux.dev> wrote:
>
> From: Andrey Konovalov <andreyknvl@google.com>
>
> Now that stack_trace_save_shadow() is implemented by arm64, use it
> whenever CONFIG_HAVE_SHADOW_STACKTRACE is enabled. This improves the
> boot time of a defconfig build by ~30% for all KASAN modes.
>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
> ---
>  mm/kasan/common.c | 9 ++++++---
>  1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/mm/kasan/common.c b/mm/kasan/common.c
> index d9079ec11f31..8d9d35c6562b 100644
> --- a/mm/kasan/common.c
> +++ b/mm/kasan/common.c
> @@ -33,10 +33,13 @@
>  depot_stack_handle_t kasan_save_stack(gfp_t flags, bool can_alloc)
>  {
>         unsigned long entries[KASAN_STACK_DEPTH];
> -       unsigned int nr_entries;
> +       unsigned int size;

Why did this variable name change?

> -       nr_entries = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> -       return __stack_depot_save(entries, nr_entries, flags, can_alloc);
> +       if (IS_ENABLED(CONFIG_HAVE_SHADOW_STACKTRACE))

Would it be more reliable to check the return-code? I.e. do:

  int size;

  size = stack_trace_save_shadow(...)
  if (size < 0)
    size = stack_trace_save(...);

> +               size = stack_trace_save_shadow(entries, ARRAY_SIZE(entries), 0);
> +       else
> +               size = stack_trace_save(entries, ARRAY_SIZE(entries), 0);
> +       return __stack_depot_save(entries, size, flags, can_alloc);
>  }
>
>  void kasan_set_track(struct kasan_track *track, gfp_t flags)
> --
> 2.25.1