linux-kernel - [PATCH] rust: drm: Improve safety comment when using `Pin::into_inner

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Message-Id: <20251226-drm-gem-safety-comment-v1-1-5ae56d8194b9@ik.me>
Date: Fri, 26 Dec 2025 18:22:36 +0100
From: Ewan Chorynski via B4 Relay <devnull+ewan.chorynski.ik.me@...nel.org>
To: David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
 Danilo Krummrich <dakr@...nel.org>, Alice Ryhl <aliceryhl@...gle.com>, 
 Miguel Ojeda <ojeda@...nel.org>, Boqun Feng <boqun.feng@...il.com>, 
 Gary Guo <gary@...yguo.net>, 
 Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>, 
 Trevor Gross <tmgross@...ch.edu>
Cc: dri-devel@...ts.freedesktop.org, rust-for-linux@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Ewan Chorynski <ewan.chorynski@...me>
Subject: [PATCH] rust: drm: Improve safety comment when using
 `Pin::into_inner_unchecked`

From: Ewan Chorynski <ewan.chorynski@...me>

The safety requirements for `Pin::into_inner_unchecked` state that the
returned pointer must be treated as pinned until it is dropped. Such a
guarantee is provided by the `ARef` type. This patch improve the safety
comment to to better reflect this.

---
Signed-off-by: Ewan Chorynski <ewan.chorynski@...me>
---
 rust/kernel/drm/gem/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/rust/kernel/drm/gem/mod.rs b/rust/kernel/drm/gem/mod.rs
index a7f682e95c01..ed11d9c0f427 100644
--- a/rust/kernel/drm/gem/mod.rs
+++ b/rust/kernel/drm/gem/mod.rs
@@ -210,7 +210,7 @@ pub fn new(dev: &drm::Device<T::Driver>, size: usize) -> Result<ARef<Self>> {
         // SAFETY: The arguments are all valid per the type invariants.
         to_result(unsafe { bindings::drm_gem_object_init(dev.as_raw(), obj.obj.get(), size) })?;
 
-        // SAFETY: We never move out of `Self`.
+        // SAFETY: We will never move out of `Self` as `ARef<Self>` is always treated as pinned.
         let ptr = KBox::into_raw(unsafe { Pin::into_inner_unchecked(obj) });
 
         // SAFETY: `ptr` comes from `KBox::into_raw` and hence can't be NULL.

---
base-commit: 6c8e404891e1059564d1a15a71d3d76070304dde
change-id: 20251226-drm-gem-safety-comment-1152e457575f

Best regards,
-- 
Ewan Chorynski <ewan.chorynski@...me>