Re: [PATCH 1/2] rust: list: fix SAFETY comment in List::remove

[Alice Ryhl <aliceryhl@google.com>]

On Tue, Apr 07, 2026 at 12:56:52PM +0100, Gary Guo wrote:
> On Tue Apr 7, 2026 at 9:15 AM BST, Alice Ryhl wrote:
> > On Fri, Apr 03, 2026 at 10:08:15PM +0000, Christian Benton wrote:
> >> The SAFETY comment for the call to ListLinks::fields in List::remove
> >> was left as TODO. Fill it in: the call is safe because T::view_links
> >> returns a reference to the ListLinks field of item, and references are
> >> always valid and non-dangling.
> >> 
> >> Signed-off-by: Christian Benton <t1bur0n.kernel.org@protonmail.ch>
> >
> > Thanks. I agree that `item` being a reference is the only thing needed
> > for this to be sound, as reference implies that the pointer is not
> > dangling.
> 
> (cc Philipp)
> 
> FWIW, I want to change `item` from a reference to a raw pointer. In Philipp's
> WIP DRM job scheduler implementation, there is a case where the list is
> conceptually a list of `UniqueArc`s; each job only needs to handle that is
> sufficient to locate the item in the list and remove it.
> 
> I suggested to him that keeping a pointer and do a list iter with ptr
> comparison is sufficient to achieve that without needing to do additional
> reference counting. Of course I don't want to iterate the list when I could just
> call `remove` function on the list itself; for that use case I want to change
> the `remove` function to only require a pointer (with additional safety
> requirement that it is valid).
> 
> It's orthogonal to this change as I'll probably be more careful about pointer
> provenance too when making that change, so just a heads up.

Could you explain why? Is there any scenario where the caller couldn't
just create a reference to the value from their raw pointer?

Alice