Messages in this thread | | | Date | Wed, 21 Apr 2021 10:43:26 +0200 | From | Michal Hocko <> | Subject | Re: [External] Re: [PATCH] mm: hugetlb: fix a race between memory-failure/soft_offline and gather_surplus_pages |
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On Wed 21-04-21 10:21:03, Oscar Salvador wrote: > On Wed, Apr 21, 2021 at 04:15:00PM +0800, Muchun Song wrote: > > > The hwpoison side of this looks really suspicious to me. It shouldn't > > > really touch the reference count of hugetlb pages without being very > > > careful (and having hugetlb_lock held). What would happen if the > > > reference count was increased after the page has been enqueed into the > > > pool? This can just blow up later. > > > > If the page has been enqueued into the pool, then the page can be > > allocated to other users. The page reference count will be reset to > > 1 in the dequeue_huge_page_node_exact(). Then memory-failure > > will free the page because of put_page(). This is wrong. Because > > there is another user. > > Note that dequeue_huge_page_node_exact() will not hand over any pages > which are poisoned, so in this case it will not be allocated.
I have to say I have missed the HWPoison check so the this particular scenario is not possible indeed.
> But it is true that we might need hugetlb lock, this needs some more > thought.
yes, nobody should be touching to the reference count of hugetlb pool pages out of the hugetlb proper.
> I will have a look.
Thanks! -- Michal Hocko SUSE Labs
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