On Wed, Sep 02, 2020 at 09:58:24AM -0700, Ralph Campbell wrote: > A migrating transparent huge page has to already be unmapped. Otherwise, > the page could be modified while it is being copied to a new page and > data could be lost. The function __split_huge_pmd() checks for a PMD > migration entry before calling __split_huge_pmd_locked() leading one to > think that __split_huge_pmd_locked() can handle splitting a migrating PMD. > However, the code always increments the page->_mapcount and adjusts the > memory control group accounting assuming the page is mapped. > Also, if the PMD entry is a migration PMD entry, the call to > is_huge_zero_pmd(*pmd) is incorrect because it calls pmd_pfn(pmd) instead > of migration_entry_to_pfn(pmd_to_swp_entry(pmd)). > Fix these problems by checking for a PMD migration entry. > > Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx> Hm. Could you remind me what codepath splits migration PMD? Maybe it should wait until migration is complete? We could avoid a lot of complexity this way. -- Kirill A. Shutemov
