Re: [linux-next:master 5585/5731] error[E0277]: `*const kernel::bindings::vm_uffd_ops` cannot be shared between threads safely

[Alice Ryhl <aliceryhl@google.com>]

On Sat, Mar 14, 2026 at 12:15:30PM +0100, Alice Ryhl wrote:
> On Sat, Mar 14, 2026 at 12:13 PM Greg Kroah-Hartman
> <gregkh@linuxfoundation.org> wrote:
> >
> > On Fri, Mar 13, 2026 at 11:39:14PM +0100, Miguel Ojeda wrote:
> > > On Fri, Mar 13, 2026 at 10:36 PM Nathan Chancellor <nathan@kernel.org> wrote:
> > > >
> > > > It looks like this is a conflict between Alice's "rust_binder: check ownership
> > > > before using vma" [1] (currently in char-misc-linus [2]) and Mike's
> > > > "userfaultfd: introduce vm_uffd_ops" [3] (currently in mm-unstable [4]),
> > > > hence why it was bisected to the -next merge commit.
> > >
> > > Thanks Nathan, yeah, adding a raw pointer (not function pointer) to
> > > the struct makes the type `!Sync` in Rust.
> > >
> > > I assume this is best handled with a patch on top of char-misc-linus.
> > > Perhaps creating a wrapper to assert it is `Sync`, since the
> > > `BINDER_VM_OPS` contents are unused (so far).
> > >
> > > Cc'ing more folks related to the commit.
> >
> > char-misc-linus should get merged into Linus's tree "soon" and then we
> > can fix up the mm-unstable change for this.
> 
> I'm working on the fix as we speak. It would be ideal if it went into
> char-misc-linus, because the commit that is wrong is mine, not the one
> in mm.

To clarify, to avoid breaking bisection, the commit needs to land
somewhere that is on top of commit 8ef2c15aeae0 ("rust_binder: check
ownership before using vma"), and before the mm commit. But I guess
there are several options for how to do that other than landing it
through char-misc-linus right now.

Alice