Messages in this thread | | | Date | Wed, 23 Aug 2023 18:35:19 +0100 | From | Gary Guo <> | Subject | Re: [PATCH 1/2] rust: arc: add explicit `drop()` around `Box::from_raw()` |
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On Wed, 23 Aug 2023 18:02:42 +0200 Miguel Ojeda <ojeda@kernel.org> wrote:
> `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>
Reviewed-by: Gary Guo <gary@garyguo.net>
> --- > 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())) }; > } > } > }
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