Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider: - [High] dma_fence: counter leak in FenceSignaler::signal causes panic on drop - [Low] rust: missing inline annotations on small forwarding functions in abstraction crate --
commit 31b644dae0c3cdaaa05c7d23cd49d1e5209e51c7 Author: Philipp Stanner <[email protected]> rust: DmaFence: [RFC] Add Signaler This commit introduces a FenceSignaler type that allows signaling an associated DriverFence independently of the locked data structure it resides in. > diff --git a/rust/kernel/dma_buf/dma_fence.rs > b/rust/kernel/dma_buf/dma_fence.rs > index b67121c7abd41..4e9b4a6a9471b 100644 > --- a/rust/kernel/dma_buf/dma_fence.rs > +++ b/rust/kernel/dma_buf/dma_fence.rs > @@ -590,6 +590,45 @@ unsafe fn dec_ref(ptr: NonNull<Self>) { > } > } > > +/// An object that can signal an associated [`DriverFence`], independently of > +/// that one's lifetime. > +/// > +/// Use with great caucion! Only the producer of a fence should ever be able > to > +/// signal it. > +/// > +/// This helper is necessary to signal DriverFences that are hidden behind > locks > +/// which cannot be taken in certain situations. > +pub struct FenceSignaler { > + fence: ARef<Fence>, > +} > + > +impl FenceSignaler { > + /// Signal the associated [`DriverFence`]. > + pub fn signal(&self, res: Result) { > + let fence = self.fence.lock(); > + > + // SAFETY: `fence` is valid because `self` is valid. The lock must be > + // held, which we acquired directly above. > + if !unsafe { bindings::dma_fence_test_signaled_flag(fence.as_raw()) > } { > + if let Err(err) = res { > + // SAFETY: `fence` is valid because `self` is valid. The > fence > + // must not have been signaled yet, which we check directly > above. > + unsafe { bindings::dma_fence_set_error(fence.as_raw(), > err.to_errno()) }; > + } > + // SAFETY: `fence` is valid because `self` is valid. The lock > must > + // be held, which we acquired above. > + unsafe { bindings::dma_fence_signal_locked(fence.as_raw()) }; > + } > + > + // TODO: This should decrement the nr-of-unsignaled-fences tracker > in fctx > + } [Severity: High] Does skipping the counter decrement here cause a resource leak leading to a kernel panic? When FenceSignaler::signal() signals the fence without decrementing nr_of_unsignaled_fences, it creates an issue during teardown. If the associated DriverFence is subsequently dropped, DriverFence::drop() will observe that the fence is already signaled and skip its own decrement: DriverFence::drop() { ... let signaled: bool = unsafe { bindings::dma_fence_test_signaled_flag(guard.as_raw()) }; if !signaled { ... } As a result, the unsignaled counter permanently leaks 1 count per use of FenceSignaler. When the FenceContext is eventually dropped, its non-zero counter triggers panic!("Forgotten fences in FenceContext."). Can this TODO be resolved before merging to prevent drivers from triggering a denial of service on normal cleanup paths? > + > + /// Get the associated fence's sequence number. > + pub fn seqno(&self) -> u64 { > + self.fence.seqno() > + } [Severity: Low] Are small forwarding functions like this missing the #[inline] attribute? According to the Rust subsystem coding guidelines, small functions or functions forwarding to a C binding call in abstractions should be annotated with #[inline] to avoid minor performance overhead across crate boundaries. [ ... ] > @@ -805,6 +844,16 @@ pub fn as_fence(&self) -> &Fence { > unsafe { Fence::from_raw(self.as_raw()) } > } > > + /// Create a [`FenceSignaler`] associated with this `DriverFence`. > + /// > + /// Use with caution! Only the producer of a [`DriverFence`] should be > able > + /// to signal it. > + pub fn new_signaler(&self) -> FenceSignaler { > + FenceSignaler { > + fence: ARef::from(self.as_fence()), > + } > + } [Severity: Low] Should this small constructor also have an #[inline] annotation? Additionally, FenceContext::deref() is a trivial deref implementation in this file missing the #[inline] attribute. Could these annotations be added? -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=4
