Re: [PATCH v4 0/1] Use HMM for ODP v4

[Jason Gunthorpe]

On Wed, May 22, 2019 at 01:48:52PM -0400, Jerome Glisse wrote:

>  static void put_per_mm(struct ib_umem_odp *umem_odp)
>  {
>  	struct ib_ucontext_per_mm *per_mm = umem_odp->per_mm;
> @@ -325,9 +283,10 @@ static void put_per_mm(struct ib_umem_odp *umem_odp)
>  	up_write(&per_mm->umem_rwsem);
>  
>  	WARN_ON(!RB_EMPTY_ROOT(&per_mm->umem_tree.rb_root));
> -	mmu_notifier_unregister_no_release(&per_mm->mn, per_mm->mm);
> +	hmm_mirror_unregister(&per_mm->mirror);
>  	put_pid(per_mm->tgid);
> -	mmu_notifier_call_srcu(&per_mm->rcu, free_per_mm);
> +
> +	kfree(per_mm);

Notice that mmu_notifier only uses SRCU to fence in-progress ops
callbacks, so I think hmm internally has the bug that this ODP
approach prevents.

hmm should follow the same pattern ODP has and 'kfree_srcu' the hmm
struct, use container_of in the mmu_notifier callbacks, and use the
otherwise vestigal kref_get_unless_zero() to bail: