Re: [RFC PATCH v10 mm-new 6/9] bpf: mark mm->owner as __safe_rcu_or_null

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

On Thu, Oct 16, 2025 at 02:42:43PM +0800, Yafang Shao wrote:
> On Thu, Oct 16, 2025 at 12:36 AM Andrii Nakryiko
> <andrii.nakryiko@gmail.com> wrote:
> >
> > On Wed, Oct 15, 2025 at 7:18 AM Yafang Shao <laoar.shao@gmail.com> wrote:
> > >
> > > When CONFIG_MEMCG is enabled, we can access mm->owner under RCU. The
> > > owner can be NULL. With this change, BPF helpers can safely access
> > > mm->owner to retrieve the associated task from the mm. We can then make
> > > policy decision based on the task attribute.
> > >
> > > The typical use case is as follows,
> > >
> > >   bpf_rcu_read_lock(); // rcu lock must be held for rcu trusted field
> > >   @owner = @mm->owner; // mm_struct::owner is rcu trusted or null
> > >   if (!@owner)
> > >       goto out;
> > >
> > >   /* Do something based on the task attribute */
> > >
> > > out:
> > >   bpf_rcu_read_unlock();
> > >
> > > Suggested-by: Andrii Nakryiko <andrii@kernel.org>
> > > Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> > > Acked-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> > > ---
> > >  kernel/bpf/verifier.c | 3 +++
> > >  1 file changed, 3 insertions(+)
> > >
> >
> > I thought you were going to send this and next patches outside of your
> > thp patch set to land them sooner, as they don't have dependency on
> > the rest of the patches and are useful on their own?
>
> Thanks for your reminder.
> They have been sent separately:
>
>   https://lore.kernel.org/bpf/20251016063929.13830-1-laoar.shao@gmail.com/

Could we respin this as a v2 without them then please so we can sensibly keep
the two separate?

Thanks!

>
> --
> Regards
> Yafang

I do intend to have a look through the various conversations on this, just
catching up after 2 weeks vacation :) in the kernel this is an eternity, even
during the merge window it seems :P

Cheers, Lorenzo