6.6-stable review patch. If anyone has any objections, please let me know.
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From: Miguel Ojeda ojeda@kernel.org
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::<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] Reviewed-by: Martin Rodriguez Reboredo yakoyoku@gmail.com Reviewed-by: Gary Guo gary@garyguo.net Reviewed-by: Alice Ryhl aliceryhl@google.com Reviewed-by: Andreas Hindborg a.hindborg@samsung.com Reviewed-by: Björn Roy Baron bjorn3_gh@protonmail.com Link: https://lore.kernel.org/r/20230823160244.188033-2-ojeda@kernel.org Signed-off-by: Miguel Ojeda ojeda@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- rust/kernel/sync/arc.rs | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/rust/kernel/sync/arc.rs +++ b/rust/kernel/sync/arc.rs @@ -302,7 +302,7 @@ impl<T: ?Sized> Drop for Arc<T> { // 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())) }; } } }