linux-kernel - [PATCH 4/9] rust: sync: Add #[must_use] to Lock::try

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Message-Id: <20250716144818.47650-5-boqun.feng@gmail.com>
Date: Wed, 16 Jul 2025 07:48:13 -0700
From: Boqun Feng <boqun.feng@...il.com>
To: Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>
Cc: "Will Deacon" <will@...nel.org>,
	"Waiman Long" <longman@...hat.com>,
	Miguel Ojeda <ojeda@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>,
	linux-kernel@...r.kernel.org,
	rust-for-linux@...r.kernel.org,
	Breno Leitao <leitao@...ian.org>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Jason Devers <dev.json2@...il.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: [PATCH 4/9] rust: sync: Add #[must_use] to Lock::try_lock()

From: Jason Devers <dev.json2@...il.com>

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@...gle.com>
Link: https://github.com/Rust-for-Linux/linux/issues/1133
Signed-off-by: Jason Devers <dev.json2@...il.com>
Reviewed-by: Alice Ryhl <aliceryhl@...gle.com>
Signed-off-by: Boqun Feng <boqun.feng@...il.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 e82fa5be289c..27202beef90c 100644
--- a/rust/kernel/sync/lock.rs
+++ b/rust/kernel/sync/lock.rs
@@ -175,6 +175,8 @@ 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.
+    // `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.
-- 
2.39.5 (Apple Git-154)