On Mon, May 22, 2017 at 02:36:00PM +0100, Punit Agrawal wrote: > When speculatively taking references to a hugepage using > page_cache_add_speculative() in gup_huge_pmd(), it is assumed that the > page returned by pmd_page() is the head page. Although normally true, > this assumption doesn't hold when the hugepage comprises of successive > page table entries such as when using contiguous bit on arm64 at PTE or > PMD levels. > > This can be addressed by ensuring that the page passed to > page_cache_add_speculative() is the real head or by de-referencing the > head page within the function. > > We take the first approach to keep the usage pattern aligned with > page_cache_get_speculative() where users already pass the appropriate > page, i.e., the de-referenced head. > > Apply the same logic to fix gup_huge_[pud|pgd]() as well. Hm. Okay. But I'm kinda surprise that this is the only place that need to be adjusted. Have you validated all other pmd_page() use-cases? -- Kirill A. Shutemov
