On Wed, Jul 3, 2019, 10:14 PM Shakeel Butt <shakeelb@google.com> wrote:

> On Tue, Jul 2, 2019 at 11:03 PM Vitaly Wool <vitalywool@gmail.com> wrote:
> >
> > On Tue, Jul 2, 2019 at 6:57 PM Henry Burns <henryburns@google.com>
> wrote:
> > >
> > > On Tue, Jul 2, 2019 at 12:45 AM Vitaly Wool <vitalywool@gmail.com>
> wrote:
> > > >
> > > > Hi Henry,
> > > >
> > > > On Mon, Jul 1, 2019 at 8:31 PM Henry Burns <henryburns@google.com>
> wrote:
> > > > >
> > > > > Running z3fold stress testing with address sanitization
> > > > > showed zhdr->slots was being used after it was freed.
> > > > >
> > > > > z3fold_free(z3fold_pool, handle)
> > > > >   free_handle(handle)
> > > > >     kmem_cache_free(pool->c_handle, zhdr->slots)
> > > > >   release_z3fold_page_locked_list(kref)
> > > > >     __release_z3fold_page(zhdr, true)
> > > > >       zhdr_to_pool(zhdr)
> > > > >         slots_to_pool(zhdr->slots)  *BOOM*
> > > >
> > > > Thanks for looking into this. I'm not entirely sure I'm all for
> > > > splitting free_handle() but let me think about it.
> > > >
> > > > > Instead we split free_handle into two functions, release_handle()
> > > > > and free_slots(). We use release_handle() in place of
> free_handle(),
> > > > > and use free_slots() to call kmem_cache_free() after
> > > > > __release_z3fold_page() is done.
> > > >
> > > > A little less intrusive solution would be to move backlink to pool
> > > > from slots back to z3fold_header. Looks like it was a bad idea from
> > > > the start.
> > > >
> > > > Best regards,
> > > >    Vitaly
> > >
> > > We still want z3fold pages to be movable though. Wouldn't moving
> > > the backink to the pool from slots to z3fold_header prevent us from
> > > enabling migration?
> >
> > That is a valid point but we can just add back pool pointer to
> > z3fold_header. The thing here is, there's another patch in the
> > pipeline that allows for a better (inter-page) compaction and it will
> > somewhat complicate things, because sometimes slots will have to be
> > released after z3fold page is released (because they will hold a
> > handle to another z3fold page). I would prefer that we just added back
> > pool to z3fold_header and changed zhdr_to_pool to just return
> > zhdr->pool, then had the compaction patch valid again, and then we
> > could come back to size optimization.
> >
>
> By adding pool pointer back to z3fold_header, will we still be able to
> move/migrate/compact the z3fold pages?l
>

Sure, it's only zhdr_to_pool() that will change, basically.

~Vitaly