On Wed, May 06, 2026 at 09:51:22AM -0400, Joel Fernandes wrote:
> The C maple_tree struct contains a *mut c_void, which prevents Rust from
> auto-deriving Send/Sync. Following is an example error message when using
> MapleTree in nova-core's Vmm.
>
> This propagates up through MapleTreeAlloc to Vmm, BarUser, Gpu, and NovaCore,
> causing NovaCore to fail the Send bound required by pci::Driver:
>
> error[E0277]: `*mut c_void` cannot be sent between threads safely
> --> drivers/gpu/nova-core/driver.rs:77:22
> |
> 77 | impl pci::Driver for NovaCore {
> | ^^^^^^^^ `*mut c_void` cannot be sent between
> threads safely
> |
> = help: within `MapleTreeAlloc<()>`, the trait `Send` is not
> implemented for `*mut c_void`
> note: required because it appears within the type
> `kernel::bindings::maple_tree`
> note: required because it appears within the type
> `Opaque<kernel::bindings::maple_tree>`
> note: required because it appears within the type `MapleTree<()>`
> note: required because it appears within the type `MapleTreeAlloc<()>`
> = note: required for `Box<MapleTreeAlloc<()>, Kmalloc>` to implement
> `Send`
> note: required because it appears within the type
> `core::pin::Pin<Box<MapleTreeAlloc<()>, Kmalloc>>`
> note: required because it appears within the type `Vmm`
> note: required because it appears within the type `BarUser`
> note: required because it appears within the type `Gpu`
> note: required because it appears within the type `NovaCore`
> note: required by a bound in `kernel::pci::Driver`
> --> rust/kernel/pci.rs:294:19
>
> Implement Send and Sync for MapleTree. The tree contains no thread-local
> state, and all shared access goes through the internal ma_lock spinlock.
>
> Signed-off-by: Joel Fernandes <[email protected]>
Reviewed-by: Alice Ryhl <[email protected]>
