From 8300dc9472edda41fe6f9b8db8877d8502b4e151 Mon Sep 17 00:00:00 2001 From: Miguel Ojeda Date: Wed, 23 Aug 2023 18:02:42 +0200 Subject: [PATCH] rust: arc: add explicit `drop()` around `Box::from_raw()` MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit commit 828176d037e29f813792a8b3ac1591834240e96f upstream. `Box::from_raw()` is `#[must_use]`, which means the result cannot go unused. In Rust 1.71.0, this was not detected because the block expression swallows the diagnostic [1]: unsafe { Box::from_raw(self.ptr.as_ptr()) }; It would have been detected, however, if the line had been instead: unsafe { Box::from_raw(self.ptr.as_ptr()); } i.e. the semicolon being inside the `unsafe` block, rather than outside. In Rust 1.72.0, the compiler started warning about this [2], so without this patch we will get: error: unused return value of `alloc::boxed::Box::::from_raw` that must be used --> rust/kernel/sync/arc.rs:302:22 | 302 | unsafe { Box::from_raw(self.ptr.as_ptr()) }; | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | = note: call `drop(Box::from_raw(ptr))` if you intend to drop the `Box` = note: `-D unused-must-use` implied by `-D warnings` help: use `let _ = ...` to ignore the resulting value | 302 | unsafe { let _ = Box::from_raw(self.ptr.as_ptr()); }; | +++++++ + Thus add an add an explicit `drop()` as the `#[must_use]`'s annotation suggests (instead of the more general help line). Link: https://github.com/rust-lang/rust/issues/104253 [1] Link: https://github.com/rust-lang/rust/pull/112529 [2] Reviewed-by: Martin Rodriguez Reboredo Reviewed-by: Gary Guo Reviewed-by: Alice Ryhl Reviewed-by: Andreas Hindborg Reviewed-by: Björn Roy Baron Link: https://lore.kernel.org/r/20230823160244.188033-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda Signed-off-by: Greg Kroah-Hartman --- rust/kernel/sync/arc.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/rust/kernel/sync/arc.rs b/rust/kernel/sync/arc.rs index 3d496391a9bd8..7f04e4f00a2c7 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -302,7 +302,7 @@ impl Drop for Arc { // The count reached zero, we must free the memory. // // SAFETY: The pointer was initialised from the result of `Box::leak`. - unsafe { Box::from_raw(self.ptr.as_ptr()) }; + unsafe { drop(Box::from_raw(self.ptr.as_ptr())) }; } } }