On Wed, 17 Feb 2021 10:49:25 -0800 Mike Kravetz <mike.kravetz@xxxxxxxxxx> wrote: > page structs are not guaranteed to be contiguous for gigantic pages. The > routine update_and_free_page can encounter a gigantic page, yet it assumes > page structs are contiguous when setting page flags in subpages. > > If update_and_free_page encounters non-contiguous page structs, we can > see “BUG: Bad page state in process …” errors. > > Non-contiguous page structs are generally not an issue. However, they can > exist with a specific kernel configuration and hotplug operations. For > example: Configure the kernel with CONFIG_SPARSEMEM and > !CONFIG_SPARSEMEM_VMEMMAP. Then, hotplug add memory for the area where the > gigantic page will be allocated. > Zi Yan outlined steps to reproduce here [1]. > > [1] https://lore.kernel.org/linux-mm/16F7C58B-4D79-41C5-9B64-A1A1628F4AF2@xxxxxxxxxx/ > > Fixes: 944d9fec8d7a ("hugetlb: add support for gigantic page allocation at runtime") June 2014. That's a long lurk time for a bug. I wonder if some later commit revealed it. I guess it doesn't matter a lot, but some -stable kernel maintainers might wonder if they really need this fix...
