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rust: delete ForeignOwnable::borrow_mut

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We discovered that the current design of `borrow_mut` is problematic.
This patch removes it until a better solution can be found.

Specifically, the current design gives you access to a `&mut T`, which
lets you change where the `ForeignOwnable` points (e.g., with
`core::mem::swap`). No upcoming user of this API intended to make that
possible, making all of them unsound.

Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Gary Guo <gary@garyguo.net>
Reviewed-by: Benno Lossin <benno.lossin@proton.me>
Reviewed-by: Martin Rodriguez Reboredo <yakoyoku@gmail.com>
Fixes: 0fc4424d24 ("rust: types: introduce `ForeignOwnable`")
Link: https://lore.kernel.org/r/20230706094615.3080784-1-aliceryhl@google.com
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
This commit is contained in:
Alice Ryhl 2023-07-06 09:46:15 +00:00 committed by Miguel Ojeda
parent b3d8aa84bb
commit 1d24eb2d53
2 changed files with 3 additions and 22 deletions
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3
rust/kernel/sync/arc.rs
View File

@ -243,8 +243,7 @@ unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> ArcBorrow<'a, T> {
let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
// SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
// for the lifetime of the returned value. Additionally, the safety requirements of
// `ForeignOwnable::borrow_mut` ensure that no new mutable references are created.
// for the lifetime of the returned value.
unsafe { ArcBorrow::new(inner) }
}

22
rust/kernel/types.rs
View File

@ -35,34 +35,16 @@ pub trait ForeignOwnable: Sized {
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow_mut`]
/// for this object must have been dropped.
unsafe fn borrow<'a>(ptr: *const core::ffi::c_void) -> Self::Borrowed<'a>;
/// Mutably borrows a foreign-owned object.
///
/// # Safety
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
/// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
unsafe fn borrow_mut(ptr: *const core::ffi::c_void) -> ScopeGuard<Self, fn(Self)> {
// SAFETY: The safety requirements ensure that `ptr` came from a previous call to
// `into_foreign`.
ScopeGuard::new_with_data(unsafe { Self::from_foreign(ptr) }, |d| {
d.into_foreign();
})
}
/// Converts a foreign-owned object back to a Rust-owned one.
///
/// # Safety
///
/// `ptr` must have been returned by a previous call to [`ForeignOwnable::into_foreign`] for
/// which a previous matching [`ForeignOwnable::from_foreign`] hasn't been called yet.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] and
/// [`ForeignOwnable::borrow_mut`] for this object must have been dropped.
/// Additionally, all instances (if any) of values returned by [`ForeignOwnable::borrow`] for
/// this object must have been dropped.
unsafe fn from_foreign(ptr: *const core::ffi::c_void) -> Self;
}