Re: [PATCH 2/3] stackdepot: use gfp_nested_mask() instead of open coded masking

[Marco Elver <elver@google.com>]

On Tue, 30 Apr 2024 at 07:46, Dave Chinner <david@fromorbit.com> wrote:
>
> From: Dave Chinner <dchinner@redhat.com>
>
> The stackdepot code is used by KASAN and lockdep for recoding stack
> traces. Both of these track allocation context information, and so
> their internal allocations must obey the caller allocation contexts
> to avoid generating their own false positive warnings that have
> nothing to do with the code they are instrumenting/tracking.
>
> We also don't want recording stack traces to deplete emergency
> memory reserves - debug code is useless if it creates new issues
> that can't be replicated when the debug code is disabled.
>
> Switch the stackdepot allocation masking to use gfp_nested_mask()
> to address these issues. gfp_nested_mask() also strips GFP_ZONEMASK
> naturally, so that greatly simplifies this code.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>

Reviewed-by: Marco Elver <elver@google.com>

> ---
>  lib/stackdepot.c | 11 ++---------
>  1 file changed, 2 insertions(+), 9 deletions(-)
>
> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
> index 68c97387aa54..0bbae49e6177 100644
> --- a/lib/stackdepot.c
> +++ b/lib/stackdepot.c
> @@ -624,15 +624,8 @@ depot_stack_handle_t stack_depot_save_flags(unsigned long *entries,
>          * we won't be able to do that under the lock.
>          */
>         if (unlikely(can_alloc && !READ_ONCE(new_pool))) {
> -               /*
> -                * Zero out zone modifiers, as we don't have specific zone
> -                * requirements. Keep the flags related to allocation in atomic
> -                * contexts and I/O.
> -                */
> -               alloc_flags &= ~GFP_ZONEMASK;
> -               alloc_flags &= (GFP_ATOMIC | GFP_KERNEL);
> -               alloc_flags |= __GFP_NOWARN;
> -               page = alloc_pages(alloc_flags, DEPOT_POOL_ORDER);
> +               page = alloc_pages(gfp_nested_mask(alloc_flags),
> +                               DEPOT_POOL_ORDER);
>                 if (page)
>                         prealloc = page_address(page);
>         }
> --
> 2.43.0
>