[tip: locking/core] rust: sync: Add #[must_use] to Lock::try_lock()

["tip-bot2 for Jason Devers" <tip-bot2@linutronix.de>]

The following commit has been merged into the locking/core branch of tip:

Commit-ID:     99214efedea521f1b79fa2a28ff142e933fc3eba
Gitweb:        https://git.kernel.org/tip/99214efedea521f1b79fa2a28ff142e933fc3eba
Author:        Jason Devers <dev.json2@gmail.com>
AuthorDate:    Thu, 12 Dec 2024 10:47:53 -05:00
Committer:     Boqun Feng <boqun.feng@gmail.com>
CommitterDate: Fri, 11 Jul 2025 15:11:54 -07:00

rust: sync: Add #[must_use] to Lock::try_lock()

The `Lock::try_lock()` function returns an `Option<Guard<...>>`, but it
currently does not issue a warning if the return value is unused.
To avoid potential bugs, the `#[must_use]` annotation is added to ensure
proper usage.

Note that `T` is `#[must_use]` but `Option<T>` is not.
For more context, see: https://github.com/rust-lang/rust/issues/71368.

Suggested-by: Alice Ryhl <aliceryhl@google.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1133
Signed-off-by: Jason Devers <dev.json2@gmail.com>
Reviewed-by: Alice Ryhl <aliceryhl@google.com>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/20241212154753.139563-1-dev.json2@gmail.com
---
 rust/kernel/sync/lock.rs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/rust/kernel/sync/lock.rs b/rust/kernel/sync/lock.rs
index e82fa5b..27202be 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -175,6 +175,8 @@ impl<T: ?Sized, B: Backend> Lock<T, B> {
     /// Tries to acquire the lock.
     ///
     /// Returns a guard that can be used to access the data protected by the lock if successful.
+    // `Option<T>` is not `#[must_use]` even if `T` is, thus the attribute is needed here.
+    #[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.