On Mon, Apr 04, 2016 at 02:03:54PM +0200, Vlastimil Babka wrote: > [+CC Andrea] > > On 04/02/2016 11:48 AM, Dmitry Vyukov wrote: > >Hello, > > > >The following program triggers a BUG in khugepaged_scan_mm_slot: > > > > > >vma ffff880032698f90 start 0000000020c57000 end 0000000020c58000 > >next ffff88003269a1b8 prev ffff88003269ac18 mm ffff88005e274780 > >prot 35 anon_vma ffff88003182c000 vm_ops (null) > >pgoff fed00 file ffff8800324552c0 private_data (null) > >flags: 0x5144477(read|write|exec|mayread|maywrite|mayexec|pfnmap|io|dontexpand|account) > >------------[ cut here ]------------ > >kernel BUG at mm/huge_memory.c:2313! > >invalid opcode: 0000 [#1] SMP DEBUG_PAGEALLOC KASAN > > That's VM_BUG_ON_VMA(vma->vm_flags & VM_NO_THP, vma) in > hugepage_vma_check(). > > #define VM_NO_THP (VM_SPECIAL | VM_HUGETLB | VM_SHARED | VM_MAYSHARE) > > #define VM_SPECIAL (VM_IO | VM_DONTEXPAND | VM_PFNMAP | VM_MIXEDMAP) > > Of those, we have VM_IO | VM_DONTEXPAND. > > I don't know if it's valid for a vma with anon_vma to have such flags, if > yes, we should probably modify hugepage_vma_check(). Called from > khugepaged_scan_mm_slot() it should just return false out VM_NO_THP. Called > from collapse_huge_page() it could keep the VM_BUG_ON. Or maybe just have > VM_BUG_ON(!hugepage_vma_check()) there? Hmm actually no, there's a mmap_sem > release for read and then acquire for write, so we can't rely on the check > done earlier from khugepaged_scan_mm_slot(). > > So we should probably just change the VM_BUG_ON to another "return false" > condition. Unless the VM_BUG_ON uncovered a real bug and the earlier > conditions in hugepage_vma_check() should guarantee the VM_BUG_ON be false > for any vma. http://lkml.kernel.org/r/145961146490.28194.16019687861681349309.stgit@zurg -- Kirill A. Shutemov -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>