Re: [PATCH] samples: rust: debugfs: fix excessive stack use

[Alexandre Courbot]

On Thu Jul 16, 2026 at 7:41 AM PDT, Gary Guo wrote:
> From: Gary Guo <gary@xxxxxxxxxxx>
>
> The current implementation creates a 4K array and move it into the box.
> Klint reports that this causes excesssive stack usage:
>
> warning: stack size of `create_file_write` is 4472 bytes, exceeds the 2048-byte limit
>   --> samples/rust/rust_debugfs_scoped.rs:54:1
>    |
> 54 | / fn create_file_write(
> 55 | |     mod_data: &ModuleData,
> 56 | |     reader: &mut kernel::uaccess::UserSliceReader,
> 57 | | ) -> Result {
>    | |___________^
>    |
>    = note: the stack size is inferred from instruction `sub $0x1178,%rsp` at .text+2205
>
> Use pin-init to create the array in-place instead.
>
> Fixes: f656279afde1 ("samples: rust: debugfs_scoped: add example for blobs")
> Signed-off-by: Gary Guo <gary@xxxxxxxxxxx>
> ---
>  samples/rust/rust_debugfs_scoped.rs | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/samples/rust/rust_debugfs_scoped.rs b/samples/rust/rust_debugfs_scoped.rs
> index 6a575a15a2c2..33a4a0865f5b 100644
> --- a/samples/rust/rust_debugfs_scoped.rs
> +++ b/samples/rust/rust_debugfs_scoped.rs
> @@ -75,7 +75,7 @@ fn create_file_write(
>              GFP_KERNEL,
>          )?;
>      }
> -    let blob = KBox::pin_init(new_mutex!([0x42; SZ_4K]), GFP_KERNEL)?;
> +    let blob = KBox::pin_init(new_mutex!(pin_init::init_array_from_fn(|_| 0x42)), GFP_KERNEL)?;

Since this is a sample, do we want to specify the size explicitly as it
is arguably more readable in this case?

Regardless,

Reviewed-by: Alexandre Courbot <acourbot@xxxxxxxxxx>