Messages in this thread Patch in this message | | | From | Miguel Ojeda <> | Subject | [PATCH 1/2] rust: arc: add explicit `drop()` around `Box::from_raw()` | Date | Wed, 23 Aug 2023 18:02:42 +0200 |
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`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::<T>::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] Signed-off-by: Miguel Ojeda <ojeda@kernel.org> --- 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 172f563976a9..4c14d540a581 100644 --- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -299,7 +299,7 @@ fn drop(&mut self) { // 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())) }; } } } -- 2.42.0
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