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Miller" , Greg Kroah-Hartman , "Liam R. Howlett" , linux-mm@kvack.org, Lorenzo Stoakes , netdev@vger.kernel.org, Shakeel Butt , Suren Baghdasaryan , Todd Kjos , Vlastimil Babka Content-Type: text/plain; charset="utf-8" On Wed, Jun 10, 2026 at 04:04:11PM -0700, Dave Hansen wrote: > --- a/rust/kernel/mm.rs~unconditional-vma-locks 2026-06-10 15:57:54.051368539 -0700 > +++ b/rust/kernel/mm.rs 2026-06-10 15:57:54.078369499 -0700 > @@ -174,7 +174,6 @@ impl MmWithUser { > /// When per-vma locks are disabled, this always returns `None`. > #[inline] > pub fn lock_vma_under_rcu(&self, vma_addr: usize) -> Option> { > - #[cfg(CONFIG_PER_VMA_LOCK)] > { > // SAFETY: Calling `bindings::lock_vma_under_rcu` is always okay given an mm where > // `mm_users` is non-zero. > @@ -188,12 +187,6 @@ impl MmWithUser { > }); > } > } > - > - // Silence warnings about unused variables. > - #[cfg(not(CONFIG_PER_VMA_LOCK))] > - let _ = vma_addr; > - > - None This isn't quite right: error[E0317]: `if` may be missing an `else` clause --> rust/kernel/mm.rs:181:13 | 181 | / if !vma.is_null() { 182 | | return Some(VmaReadGuard { ... | 187 | | }); 188 | | } | |_____________^ expected `Option>`, found `()` | = note: expected enum `core::option::Option>` found unit type `()` = note: `if` expressions without `else` evaluate to `()` = help: consider adding an `else` block that evaluates to the expected type This error is triggered because you deleted the return 'None' at the end of the function. I would like to suggest the following implementation // SAFETY: Calling `bindings::lock_vma_under_rcu` is always okay given an mm where // `mm_users` is non-zero. let vma = unsafe { bindings::lock_vma_under_rcu(self.as_raw(), vma_addr) }; if vma.is_null() { return None; } Some(VmaReadGuard { // SAFETY: If `lock_vma_under_rcu` returns a non-null ptr, then it points at a valid // vma. The vma is stable for as long as the vma read lock is held. vma: unsafe { VmaRef::from_raw(vma) }, _nts: NotThreadSafe, }) Thanks! Alice