Previously, `KBox::pin_slice` required the initializer error type to match the return error type via `E: From<AllocError>`. This prevented using infallible initializers like `new_mutex!` inside `pin_slice`, because `Infallible` does not implement `From<AllocError>`. Introduce a separate type parameter `E2` for the initializer error type and require `E: From<AllocError>` and `E: From<E2>` instead. This allows the initializer to return a different error type that can be converted into the final error type, enabling use of infallible pin initializers in fallible allocation contexts. Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/.E2.9C.94.20Constructing.20Mutex.20from.20PinInit.3CT.2C.20Error.3E Co-developed-by: Benno Lossin <lossin@kernel.org> Signed-off-by: Benno Lossin <lossin@kernel.org> Signed-off-by: Andreas Hindborg <a.hindborg@kernel.org> Link: https://patch.msgid.link/20260605-pin-slice-init-v2-1-b197e84040ba@kernel.org Signed-off-by: Danilo Krummrich <dakr@kernel.org>