Re: [PATCH 11/12] device-dax: Add dis-contiguous resource support

[Dan Williams]

On Mon, Apr 6, 2020 at 3:46 AM Joao Martins <joao.m.martins@xxxxxxxxxx> wrote:
>
> On 3/23/20 11:55 PM, Dan Williams wrote:
>
> [...]
>
> >  static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >               struct dev_dax *dev_dax, resource_size_t size)
> >  {
> >       resource_size_t avail = dax_region_avail_size(dax_region), to_alloc;
> > -     resource_size_t dev_size = range_len(&dev_dax->range);
> > +     resource_size_t dev_size = dev_dax_size(dev_dax);
> >       struct resource *region_res = &dax_region->res;
> >       struct device *dev = &dev_dax->dev;
> > -     const char *name = dev_name(dev);
> >       struct resource *res, *first;
> > +     resource_size_t alloc = 0;
> > +     int rc;
> >
> >       if (dev->driver)
> >               return -EBUSY;
> > @@ -684,38 +766,47 @@ static ssize_t dev_dax_resize(struct dax_region *dax_region,
> >        * allocating a new resource.
> >        */
> >       first = region_res->child;
> > -     if (!first)
> > -             return __alloc_dev_dax_range(dev_dax, dax_region->res.start,
> > -                             to_alloc);
> > -     for (res = first; to_alloc && res; res = res->sibling) {
> > +retry:
> > +     rc = -ENOSPC;
> > +     for (res = first; res; res = res->sibling) {
> >               struct resource *next = res->sibling;
> > -             resource_size_t free;
> >
> >               /* space at the beginning of the region */
> > -             free = 0;
> > -             if (res == first && res->start > dax_region->res.start)
> > -                     free = res->start - dax_region->res.start;
> > -             if (free >= to_alloc && dev_size == 0)
> > -                     return __alloc_dev_dax_range(dev_dax,
> > -                                     dax_region->res.start, to_alloc);
> > -
> > -             free = 0;
> > +             if (res == first && res->start > dax_region->res.start) {
> > +                     alloc = min(res->start - dax_region->res.start,
> > +                                     to_alloc);
> > +                     rc = __alloc_dev_dax_range(dev_dax,
> > +                                     dax_region->res.start, alloc);
>
> You might be missing:
>
>         first = region_res->child;
>
> (...) right after returning from __alloc_dev_dax_range(). Alternatively, perhaps
> even moving the 'retry' label to right before the @first initialization.
>
> In the case that you pick space from the beginning, the child resource of the
> dax region will point to first occupied region, and that changes after you pick
> this space. So, IIUC, you want to adjust where you start searching free space
> otherwise you end up wrongly picking that same space twice.
>
> If it helps, the bug can be reproduced in this unit test below, see
> daxctl_test3() test:

It definitely will, thanks. I'll be circling back to this now that
I've settled my tree for the v5.7 window.