Re: [PATCH] aio: Convert ioctx_table to XArray

[Matthew Wilcox]

On Tue, Dec 11, 2018 at 11:41:55AM -0700, Jens Axboe wrote:
> On Wed, Nov 28, 2018 at 11:35 AM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> >
> >         rcu_read_lock();
> > -       table = rcu_dereference(mm->ioctx_table);
> > -
> > -       if (!table || id >= table->nr)
> > -               goto out;
> > -
> > -       ctx = rcu_dereference(table->table[id]);
> > +       ctx = xa_load(&mm->ioctx, id);
> >         if (ctx && ctx->user_id == ctx_id) {
> >                 if (percpu_ref_tryget_live(&ctx->users))
> >                         ret = ctx;
> >         }
> 
> Question on this part - do we need that RCU read lock around this now? I
> don't think we do.

I think we need the rcu read lock here to prevent ctx from being freed
under us by free_ioctx().