diff options
| author | Alice Ryhl <aliceryhl@google.com> | 2025-06-12 11:17:33 +0000 |
|---|---|---|
| committer | Miguel Ojeda <ojeda@kernel.org> | 2025-06-29 18:54:54 +0200 |
| commit | d6763e0abb43d550791eb66d2b91e82cb29807f9 (patch) | |
| tree | 8f9a668ad2732c5424ac4bf0831ce97c6b524e28 /rust/kernel | |
| parent | fbcd4b7bf5c92f7d456eefcecac518023357cea4 (diff) | |
rust: revocable: document why &T is not used in RevocableGuard
When a reference appears in a function argument, the reference is
assumed to be valid for the entire duration of that function call; this
is called a stack protector [1]. Because of that, custom pointer types
whose destructor may invalidate the pointee (i.e. they are more similar
to Box<T> than &T) cannot internally use a reference, and must instead
use a raw pointer.
This issue is something that is often missed during unsafe review. For
examples, see [2] and [3]. To ensure that people don't try to simplify
RevocableGuard by changing the raw pointer to a reference, add a comment
to that effect.
Link: https://perso.crans.org/vanille/treebor/protectors.html [1]
Link: https://users.rust-lang.org/t/unsafe-code-review-semi-owning-weak-rwlock-t-guard/95706 [2]
Link: https://lore.kernel.org/all/aEqdur4JTFa1V20U@google.com/ [3]
Signed-off-by: Alice Ryhl <aliceryhl@google.com>
Reviewed-by: Benno Lossin <lossin@kernel.org>
Link: https://lore.kernel.org/r/20250612-revocable-ptr-comment-v1-1-db36785877f6@google.com
[ Adjusted title. - Miguel ]
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Diffstat (limited to 'rust/kernel')
| -rw-r--r-- | rust/kernel/revocable.rs | 4 |
1 files changed, 4 insertions, 0 deletions
diff --git a/rust/kernel/revocable.rs b/rust/kernel/revocable.rs index 06a3cdfce344..1cd4511f0260 100644 --- a/rust/kernel/revocable.rs +++ b/rust/kernel/revocable.rs @@ -231,6 +231,10 @@ impl<T> PinnedDrop for Revocable<T> { /// /// The RCU read-side lock is held while the guard is alive. pub struct RevocableGuard<'a, T> { + // This can't use the `&'a T` type because references that appear in function arguments must + // not become dangling during the execution of the function, which can happen if the + // `RevocableGuard` is passed as a function argument and then dropped during execution of the + // function. data_ref: *const T, _rcu_guard: rcu::Guard, _p: PhantomData<&'a ()>, |