linux-kernel - [PATCH v6 1/6] rust: arc: use `NonNull::new

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Message-Id: <20241120-borrow-mut-v6-1-80dbadd00951@gmail.com>
Date: Wed, 20 Nov 2024 06:46:00 -0500
From: Tamir Duberstein <tamird@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
 Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <benno.lossin@...ton.me>, 
 Andreas Hindborg <a.hindborg@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Trevor Gross <tmgross@...ch.edu>, Danilo Krummrich <dakr@...nel.org>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Tamir Duberstein <tamird@...il.com>
Subject: [PATCH v6 1/6] rust: arc: use `NonNull::new_unchecked`

There is no need to check (and panic on violations of) the safety
requirements on `ForeignOwnable` functions. Avoiding the check is
consistent with the implementation of `ForeignOwnable` for `Box`.

Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Reviewed-by: Andreas Hindborg <a.hindborg@...nel.org>
Signed-off-by: Tamir Duberstein <tamird@...il.com>
---
 rust/kernel/sync/arc.rs | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs
index fa4509406ee909ca0677b78d5ece966089ce6366..b4e492dd712137c7c39e3de3d39c0c833944828c 100644
--- a/rust/kernel/sync/arc.rs
+++ b/rust/kernel/sync/arc.rs
@@ -337,9 +337,9 @@ fn into_foreign(self) -> *const crate::ffi::c_void {
     }
 
     unsafe fn borrow<'a>(ptr: *const crate::ffi::c_void) -> ArcBorrow<'a, T> {
-        // By the safety requirement of this function, we know that `ptr` came from
-        // a previous call to `Arc::into_foreign`.
-        let inner = NonNull::new(ptr as *mut ArcInner<T>).unwrap();
+        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
+        // call to `Self::into_foreign`.
+        let inner = unsafe { NonNull::new_unchecked(ptr as *mut ArcInner<T>) };
 
         // SAFETY: The safety requirements of `from_foreign` ensure that the object remains alive
         // for the lifetime of the returned value.
@@ -347,10 +347,14 @@ unsafe fn borrow<'a>(ptr: *const crate::ffi::c_void) -> ArcBorrow<'a, T> {
     }
 
     unsafe fn from_foreign(ptr: *const crate::ffi::c_void) -> Self {
+        // SAFETY: The safety requirements of this function ensure that `ptr` comes from a previous
+        // call to `Self::into_foreign`.
+        let inner = unsafe { NonNull::new_unchecked(ptr as *mut ArcInner<T>) };
+
         // SAFETY: By the safety requirement of this function, we know that `ptr` came from
         // a previous call to `Arc::into_foreign`, which guarantees that `ptr` is valid and
         // holds a reference count increment that is transferrable to us.
-        unsafe { Self::from_inner(NonNull::new(ptr as _).unwrap()) }
+        unsafe { Self::from_inner(inner) }
     }
 }
 

-- 
2.47.0