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mm: turn folio_test_hugetlb into a PageType
The current folio_test_hugetlb() can be fooled by a concurrent folio split into returning true for a folio which has never belonged to hugetlbfs. This can't happen if the caller holds a refcount on it, but we have a few places (memory-failure, compaction, procfs) which do not and should not take a speculative reference. Since hugetlb pages do not use individual page mapcounts (they are always fully mapped and use the entire_mapcount field to record the number of mappings), the PageType field is available now that page_mapcount() ignores the value in this field. In compaction and with CONFIG_DEBUG_VM enabled, the current implementation can result in an oops, as reported by Luis. This happens since 9c5ccf2 ("mm: remove HUGETLB_PAGE_DTOR") effectively added some VM_BUG_ON() checks in the PageHuge() testing path. [[email protected]: update vmcoreinfo] Link: https://lkml.kernel.org/r/[email protected] Link: https://lkml.kernel.org/r/[email protected] Fixes: 9c5ccf2 ("mm: remove HUGETLB_PAGE_DTOR") Signed-off-by: Matthew Wilcox (Oracle) <[email protected]> Reviewed-by: David Hildenbrand <[email protected]> Acked-by: Vlastimil Babka <[email protected]> Reported-by: Luis Chamberlain <[email protected]> Closes: https://bugzilla.kernel.org/show_bug.cgi?id=218227 Cc: Miaohe Lin <[email protected]> Cc: Muchun Song <[email protected]> Cc: Oscar Salvador <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
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