On Thu 18-03-21 10:59:10, Oscar Salvador wrote:
> On Thu, Mar 18, 2021 at 10:29:57AM +0100, Michal Hocko wrote:
> > On Thu 18-03-21 09:54:01, Oscar Salvador wrote:
> > [...]
> > > @@ -2287,10 +2288,12 @@ static int alloc_and_dissolve_huge_page(struct 
> > > hstate *h, struct page *old_page)
> > >           goto unlock;
> > >   } else if (page_count(old_page)) {
> > >           /*
> > > -          * Someone has grabbed the page, fail for now.
> > > +          * Someone has grabbed the page, try to isolate it here.
> > > +          * Fail with -EBUSY if not possible.
> > >            */
> > > -         ret = -EBUSY;
> > >           update_and_free_page(h, new_page);
> > > +         if (!isolate_huge_page(old_page, list)
> > > +                 ret = -EBUSY;
> > >           goto unlock;
> > >   } else if (!HPageFreed(old_page)) {
> > 
> > I do not think you want to call isolate_huge_page with hugetlb_lock
> > held. You would need to drop the lock before calling isolate_huge_page.
> 
> Yeah, that was an oversight. As I said I did not compile it(let alone
> test it), otherwise the system would have screamed I guess.
> 
> I was more interested in knowing whether how did it look wrt. retry
> concerns:

Yes this looks much more to my taste. If we need to retry then it could
just goto retry there. The caller doesn't really have to care.

> @@ -2287,10 +2288,14 @@ static int alloc_and_dissolve_huge_page(struct hstate 
> *h, struct page *old_page)
>               goto unlock;
>       } else if (page_count(old_page)) {
>               /*
> -              * Someone has grabbed the page, fail for now.
> +              * Someone has grabbed the page, try to isolate it here.
> +              * Fail with -EBUSY if not possible.
>                */
> -             ret = -EBUSY;
>               update_and_free_page(h, new_page);
> +             spin_unlock(&hugetlb_lock);
> +             if (!isolate_huge_page(old_page, list)
> +                     ret = -EBUSY;
> +             spin_lock(&hugetlb_lock);
>               goto unlock;

simply return ret; here
-- 
Michal Hocko
SUSE Labs

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