Depending on what the JobQueue locking design shall look like, it might be necessary to be able to signal fences without having to access the *locked* data structure the fences reside in.
Add a Signaler type to achieve that. This type is not yet used in this patch series. The patch merely serves showing the idea so that we have material to discuss. Signed-off-by: Philipp Stanner <[email protected]> --- rust/kernel/dma_buf/dma_fence.rs | 49 ++++++++++++++++++++++++++++++++ 1 file changed, 49 insertions(+) diff --git a/rust/kernel/dma_buf/dma_fence.rs b/rust/kernel/dma_buf/dma_fence.rs index b67121c7abd4..4e9b4a6a9471 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 + } + + /// Get the associated fence's sequence number. + pub fn seqno(&self) -> u64 { + self.fence.seqno() + } +} + // Necessary to guarantee that `inner` always comes first and can be freed by C. // Also useful for using casts instead of container_of(). #[repr(C)] @@ -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()), + } + } + /// Signal the fence. This will invoke all registered callbacks. pub fn signal(&self, res: Result) { let fence = self.as_fence().lock(); -- 2.55.0
