Re: [PATCH] rust: sync: add #[must_use] to Lock::try_lock

[Boqun Feng <boqun.feng@gmail.com>]

Hi Jason,

Thanks for the patch.

On Sun, Dec 08, 2024 at 01:48:34PM -0500, Jason Devers wrote:
> The `Lock::try_lock` function returns an `Option<Guard<...>>`, but it
> currently does not issue a warning if the return value is unused. This
> could result in the lock being unlocked immediately, which is unsafe

I don't think not having `#[must_use]` will result in the locking being
unlocked immediately, do you have an example?

> and unintended. This patch adds a `#[must_use]` annotation to

Are you sure this is unsafe? Again do you have an example showing this?

Regards,
Boqun

> `Lock::try_lock` to prevent this.
> 
> Suggested-by: Alice Ryhl <alice@ryhl.io>
> Link: https://github.com/Rust-for-Linux/linux/issues/1133
> Signed-off-by: Jason Devers <dev.json2@gmail.com>
> ---
>  rust/kernel/sync/lock.rs | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
> index 41dcddac69e2..f6a5e83ff685 100644
> --- a/rust/kernel/sync/lock.rs
> +++ b/rust/kernel/sync/lock.rs
> @@ -147,6 +147,7 @@ pub fn lock(&self) -> Guard<'_, T, B> {
>      /// Tries to acquire the lock.
>      ///
>      /// Returns a guard that can be used to access the data protected by the lock if successful.
> +    #[must_use = "if unused, the lock will be immediately unlocked"]
>      pub fn try_lock(&self) -> Option<Guard<'_, T, B>> {
>          // SAFETY: The constructor of the type calls `init`, so the existence of the object proves
>          // that `init` was called.
> -- 
> 2.44.2
>