Re: [PATCH v2 5/6] rust: Add dma_fence abstractions

Philipp Stanner <[email protected]> Tue, 16 Jun 2026 16:38:51 +0200

Newsgroups	org.kernel.vger.rcu,org.freedesktop.lists.dri-devel,org.kernel.vger.linux-kernel,org.kernel.vger.linux-media,org.kernel.vger.rust-for-linux
Message-ID	<[email protected]>

On Tue, 2026-06-16 at 15:47 +0300, Onur Özkan wrote:
> On Tue, 16 Jun 2026 10:28:17 +0200
> > +
> > +        // DriverFenceData is repr(C) and a Fence is its first member.
> > +        let fence_data_ptr = fence_ptr as *mut DriverFenceData<T>;
> 
> Either the field ordering on the type or this code is wrong because the first
> member of DriverFenceData is `rcu_head`.

Yeah, that's a bug introduced in this revision. Thx for pointing it
out. Already fixed it downstream.

I'm just wondering why my test did not blow up.

> > 
> > +}
> 
> I am unsure whether it is safe to cast the pointer in Fence::from_raw without
> Fence being #[repr(transparent)] as the layout compatibility is not guaranteed
> explicitly.

Shouldn't #[repr(C)] do that trick, too? Do you need both?

Who can answer that?


P.