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Hugh Dickins
b38af4721f
Sasha Levin has shown oopses on ffffea0003480048 and ffffea0003480008 at mm/memory.c:1132, running Trinity on different 3.16-rc-next kernels: where zap_pte_range() checks page->mapping to see if PageAnon(page). Those addresses fit struct pages for pfns d2001 and d2000, and in each dump a register or a stack slot showed d2001730 or d2000730: pte flags 0x730 are PCD ACCESSED PROTNONE SPECIAL IOMAP; and Sasha's e820 map has a hole between cfffffff and 100000000, which would need special access. Commitc46a7c817e("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") has broken vm_normal_page(): a PROTNONE SPECIAL pte no longer passes the pte_special() test, so zap_pte_range() goes on to try to access a non-existent struct page. Fix this by refining pte_special() (SPECIAL with PRESENT or PROTNONE) to complement pte_numa() (SPECIAL with neither PRESENT nor PROTNONE). A hint that this was a problem was thatc46a7c817eadded pte_numa() test to vm_normal_page(), and moved its is_zero_pfn() test from slow to fast path: This was papering over a pte_special() snag when the zero page was encountered during zap. This patch reverts vm_normal_page() to how it was before, relying on pte_special(). It still appears that this patch may be incomplete: aren't there other places which need to be handling PROTNONE along with PRESENT? For example, pte_mknuma() clears _PAGE_PRESENT and sets _PAGE_NUMA, but on a PROT_NONE area, that would make it pte_special(). This is side-stepped by the fact that NUMA hinting faults skipped PROT_NONE VMAs and there are no grounds where a NUMA hinting fault on a PROT_NONE VMA would be interesting. Fixes:c46a7c817e("x86: define _PAGE_NUMA by reusing software bits on the PMD and PTE levels") Reported-by: Sasha Levin <[email protected]> Tested-by: Sasha Levin <[email protected]> Signed-off-by: Hugh Dickins <[email protected]> Signed-off-by: Mel Gorman <[email protected]> Cc: "Kirill A. Shutemov" <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Rik van Riel <[email protected]> Cc: Johannes Weiner <[email protected]> Cc: Cyrill Gorcunov <[email protected]> Cc: Matthew Wilcox <[email protected]> Cc: <[email protected]> [3.16] Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>