rust compile failure in next-20260730

rust compile failure in next-20260730

[Bert Karwatzki]

With next-20260730 building a kernel with CONFIG_RUST=y fails with
the following error:

 RUSTC L rust/kernel.o
error[E0308]: mismatched types
     --> rust/kernel/sync/poll.rs:175:44
      |
  175 |         unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
      |                  ------------------------- ^^^^^^^^^^^^^^^^ expected `*mut kvfree_rcu_head`, found `*mut callback_head`
      |                  |
      |                  arguments to this function are incorrect
      |
      = note: expected raw pointer `*mut bindings::kvfree_rcu_head`
                 found raw pointer `*mut bindings::callback_head`
note: function defined here
     --> /mnt/data/linux-forest/linux-next/rust/bindings/bindings_generated.rs:73708:12
      |
73708 |     pub fn kvfree_call_rcu(head: *mut kvfree_rcu_head, ptr: *mut ffi::c_void);
      |            ^^^^^^^^^^^^^^^

error: aborting due to 1 previous error

For more information about this error, try `rustc --explain E0308`.
make[5]: *** [rust/Makefile:781: rust/kernel.o] Fehler 1
make[4]: *** [Makefile:1420: prepare] Fehler 2
make[3]: *** [debian/rules:80: build-arch] Fehler 2

Reverting the following commits:
ef32a74f8f6a ("mm/slab: introduce kfree_rcu_nolock()")
bdd0cc9f0ffc ("mm/slab: introduce struct kvfree_rcu_head for kvfree_rcu batching")
    
make the compilation work again.   

Bert Karwatzki

Re: rust compile failure in next-20260730

[Thorsten Leemhuis]

On 7/31/26 14:28, Bert Karwatzki wrote:
> With next-20260730 building a kernel with CONFIG_RUST=y fails with
> the following error:

Ran into this, too. Fixing this is discussed in this thread:
https://lore.kernel.org/all/20260731075644.20215-1-ojeda@kernel.org/

>  RUSTC L rust/kernel.o
> error[E0308]: mismatched types
>      --> rust/kernel/sync/poll.rs:175:44
>       |
>   175 |         unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
>       |                  ------------------------- ^^^^^^^^^^^^^^^^ expected `*mut kvfree_rcu_head`, found `*mut callback_head`
>       |                  |
>       |                  arguments to this function are incorrect
>       |
>       = note: expected raw pointer `*mut bindings::kvfree_rcu_head`
>                  found raw pointer `*mut bindings::callback_head`
> note: function defined here
>      --> /mnt/data/linux-forest/linux-next/rust/bindings/bindings_generated.rs:73708:12
>       |
> 73708 |     pub fn kvfree_call_rcu(head: *mut kvfree_rcu_head, ptr: *mut ffi::c_void);
>       |            ^^^^^^^^^^^^^^^
> 
> error: aborting due to 1 previous error
> 
> For more information about this error, try `rustc --explain E0308`.
> make[5]: *** [rust/Makefile:781: rust/kernel.o] Fehler 1
> make[4]: *** [Makefile:1420: prepare] Fehler 2
> make[3]: *** [debian/rules:80: build-arch] Fehler 2
> 
> Reverting the following commits:
> ef32a74f8f6a ("mm/slab: introduce kfree_rcu_nolock()")
> bdd0cc9f0ffc ("mm/slab: introduce struct kvfree_rcu_head for kvfree_rcu batching")
>     
> make the compilation work again.   
> 
> Bert Karwatzki

Re: rust compile failure in next-20260730

[Luna Jernberg]

Noticed this too

Den fre 31 juli 2026 kl 15:21 skrev Thorsten Leemhuis <linux@leemhuis.info>:
>
> On 7/31/26 14:28, Bert Karwatzki wrote:
> > With next-20260730 building a kernel with CONFIG_RUST=y fails with
> > the following error:
>
> Ran into this, too. Fixing this is discussed in this thread:
> https://lore.kernel.org/all/20260731075644.20215-1-ojeda@kernel.org/
>
> >  RUSTC L rust/kernel.o
> > error[E0308]: mismatched types
> >      --> rust/kernel/sync/poll.rs:175:44
> >       |
> >   175 |         unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
> >       |                  ------------------------- ^^^^^^^^^^^^^^^^ expected `*mut kvfree_rcu_head`, found `*mut callback_head`
> >       |                  |
> >       |                  arguments to this function are incorrect
> >       |
> >       = note: expected raw pointer `*mut bindings::kvfree_rcu_head`
> >                  found raw pointer `*mut bindings::callback_head`
> > note: function defined here
> >      --> /mnt/data/linux-forest/linux-next/rust/bindings/bindings_generated.rs:73708:12
> >       |
> > 73708 |     pub fn kvfree_call_rcu(head: *mut kvfree_rcu_head, ptr: *mut ffi::c_void);
> >       |            ^^^^^^^^^^^^^^^
> >
> > error: aborting due to 1 previous error
> >
> > For more information about this error, try `rustc --explain E0308`.
> > make[5]: *** [rust/Makefile:781: rust/kernel.o] Fehler 1
> > make[4]: *** [Makefile:1420: prepare] Fehler 2
> > make[3]: *** [debian/rules:80: build-arch] Fehler 2
> >
> > Reverting the following commits:
> > ef32a74f8f6a ("mm/slab: introduce kfree_rcu_nolock()")
> > bdd0cc9f0ffc ("mm/slab: introduce struct kvfree_rcu_head for kvfree_rcu batching")
> >
> > make the compilation work again.
> >
> > Bert Karwatzki
>
>

Re: rust compile failure in next-20260730

[Nathan Chancellor]

+ folks from e5e86df8b666

On Fri, Jul 31, 2026 at 02:28:25PM +0200, Bert Karwatzki wrote:
> With next-20260730 building a kernel with CONFIG_RUST=y fails with
> the following error:
> 
>  RUSTC L rust/kernel.o
> error[E0308]: mismatched types
>      --> rust/kernel/sync/poll.rs:175:44
>       |
>   175 |         unsafe { bindings::kvfree_call_rcu((*ptr).rcu.get(), ptr.cast::<ffi::c_void>()) };
>       |                  ------------------------- ^^^^^^^^^^^^^^^^ expected `*mut kvfree_rcu_head`, found `*mut callback_head`
>       |                  |
>       |                  arguments to this function are incorrect
>       |
>       = note: expected raw pointer `*mut bindings::kvfree_rcu_head`
>                  found raw pointer `*mut bindings::callback_head`
> note: function defined here
>      --> /mnt/data/linux-forest/linux-next/rust/bindings/bindings_generated.rs:73708:12
>       |
> 73708 |     pub fn kvfree_call_rcu(head: *mut kvfree_rcu_head, ptr: *mut ffi::c_void);
>       |            ^^^^^^^^^^^^^^^
> 
> error: aborting due to 1 previous error
> 
> For more information about this error, try `rustc --explain E0308`.
> make[5]: *** [rust/Makefile:781: rust/kernel.o] Fehler 1
> make[4]: *** [Makefile:1420: prepare] Fehler 2
> make[3]: *** [debian/rules:80: build-arch] Fehler 2
> 
> Reverting the following commits:
> ef32a74f8f6a ("mm/slab: introduce kfree_rcu_nolock()")
> bdd0cc9f0ffc ("mm/slab: introduce struct kvfree_rcu_head for kvfree_rcu batching")
>     
> make the compilation work again.   

This is a collision between commit e5e86df8b666 ("rust: poll: use
kfree_rcu() for PollCondVar") in the char-misc tree and the
aforementioned commit bdd0cc9f0ffc ("mm/slab: introduce struct
kvfree_rcu_head for kvfree_rcu batching") in the slab tree.

Something like this avoids the error for me but I am not sure if it is
a proper fix.

diff --git a/rust/kernel/sync/poll.rs b/rust/kernel/sync/poll.rs
index 684dfa242b1a..5b12d5d4e9af 100644
--- a/rust/kernel/sync/poll.rs
+++ b/rust/kernel/sync/poll.rs
@@ -124,6 +124,9 @@ pub struct PollCondVarBox {
 struct PollCondVarBoxInner {
     #[pin]
     inner: PollCondVar,
+    #[cfg(CONFIG_KVFREE_RCU_BATCHED)]
+    rcu: Opaque<bindings::kvfree_rcu_head>,
+    #[cfg(not(CONFIG_KVFREE_RCU_BATCHED))]
     rcu: Opaque<bindings::callback_head>,
 }
 
-- 
Cheers,
Nathan