Re: [PATCH] [RFC] maple_tree: reduce stack usage with gcc-9 and earlier

[Andrew Morton]

On Tue, 14 Feb 2023 11:30:24 +0100 Arnd Bergmann <arnd@xxxxxxxxxx> wrote:

> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> gcc-10 changed the way inlining works to be less aggressive, but
> older versions run into an oversized stack frame warning whenever
> CONFIG_KASAN_STACK is enabled, as that forces variables from
> inlined callees to be non-overlapping:
> 
> lib/maple_tree.c: In function 'mas_wr_bnode':
> lib/maple_tree.c:4320:1: error: the frame size of 1424 bytes is larger than 1024 bytes [-Werror=frame-larger-than=]
> 
> Change the annotations on mas_store_b_node() and mas_commit_b_node()
> to explicitly forbid inlining in this configuration, which is
> the same behavior that newer versions already have.
> 
> ...
>
> --- a/lib/maple_tree.c
> +++ b/lib/maple_tree.c
> @@ -146,6 +146,13 @@ struct maple_subtree_state {
>  	struct maple_big_node *bn;
>  };
>  
> +#ifdef CONFIG_KASAN_STACK
> +/* Prevent mas_wr_bnode() from exceeding the stack frame limit */
> +#define noinline_for_kasan noinline_for_stack
> +#else
> +#define noinline_for_kasan inline
> +#endif

Should noinline_for_kasan be defined in kasan.h?  maple_tree.c is
unlikely to be the only place in the kernel which could use this
treatment?

I suppose we can do that when the need arises.