On Fri, 2026-04-24 at 00:01 +0900, Alexandre Courbot wrote:
There are 4 sites where we acquire and release the DMA resv lock, each of which require unsafe blocks and carrying the risk that we forget releasing the lock in the end. For this method in particular we need to jump through hoops a bit and store the return value into a temporary variable so we can unlock the DMA reservation.
Let's do ourselves a favor and implement a small, private guard type:
struct DmaResvGuard<'a, T: DriverObject>(&'a Object<T>);
impl<'a, T: DriverObject> DmaResvGuard<'a, T> { fn new(object: &'a Object<T>) -> Self { // SAFETY: This lock is initialized throughout the lifetime of `object` unsafe { bindings::dma_resv_lock(object.raw_dma_resv(), ptr::null_mut()) };
Self(object) } }
impl<'a, T> Drop for DmaResvGuard<'a, T> where T: DriverObject, { fn drop(&mut self) { // SAFETY: We are releasing the lock grabbed during the creation of this object. unsafe { bindings::dma_resv_unlock(self.0.raw_dma_resv()) }; } }
There here you would just do
let _dma_resv = DmaResvGuard::new(self);
I thought of doing this but lost track of how many times I was actually grabbing this lock… BTW - want me to just give you authorship on the patch for adding DmaResvGuard? Since on my branch I've pretty much only just added two inline annotations, it's otherwise identical to what you wrote here.