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

[Gary Guo]

On Thu Jul 16, 2026 at 9:33 PM BST, Alexandre Courbot wrote:
> 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?

It's not easy to specify size with `init_array_from_fn` because you need to
specify additionally Init, T and E, so it'll become

    init_array_from_fn::<_, SZ_4K, _, _>

which is ugly.

Best,
Gary