Re: [PATCH v2 1/1] mm/hugetlb: fix memory offline with hugepage size > memory block size

[Hillf Danton]

> 
> dissolve_free_huge_pages() will either run into the VM_BUG_ON() or a
> list corruption and addressing exception when trying to set a memory
> block offline that is part (but not the first part) of a hugetlb page
> with a size > memory block size.
> 
> When no other smaller hugetlb page sizes are present, the VM_BUG_ON()
> will trigger directly. In the other case we will run into an addressing
> exception later, because dissolve_free_huge_page() will not work on the
> head page of the compound hugetlb page which will result in a NULL
> hstate from page_hstate().
> 
> To fix this, first remove the VM_BUG_ON() because it is wrong, and then
> use the compound head page in dissolve_free_huge_page().
> 
> Also change locking in dissolve_free_huge_page(), so that it only takes
> the lock when actually removing a hugepage.
> 
> Signed-off-by: Gerald Schaefer <gerald.schaefer@xxxxxxxxxx>
> ---
Acked-by: Hillf Danton <hillf.zj@xxxxxxxxxxxxxxx>