Subject: linux-next: build failure after merge of the driver-core tree

From: Stephen Rothwell <[email-masked]>
Date: Fri, 7 Nov 2025 13:41:44 +1100

Hi all,

After merging the driver-core tree, today's linux-next build (x86_64
allmodconfig) failed like this:

error: variable does not need to be mutable
   --> rust/kernel/debugfs/traits.rs:266:13
    |
266 |         let mut this = self.lock();
    |             ----^^^^
    |             |
    |             help: remove this `mut`
    |
    = note: `-D unused-mut` implied by `-D warnings`
    = help: to override `-D warnings` add `#[allow(unused_mut)]`

error[E0596]: cannot borrow data in dereference of `lock::Guard<'_, T, MutexBackend>` as mutable
   --> rust/kernel/debugfs/traits.rs:268:9
    |
268 |         this.read_from_slice_mut(reader, offset)
    |         ^^^^ cannot borrow as mutable
    |
    = help: trait `DerefMut` is required to modify through a dereference, but it is not implemented for `lock::Guard<'_, T, MutexBackend>`

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0596`.

Caused by commit

  a9fca8a7b2c5 ("rust: debugfs: support blobs from smart pointers")

(maybe interacting with some other change).

I have used the driver-core tree from next-20251106 for today.

-- 
Cheers,
Stephen Rothwell