On Wed, Aug 01, 2018 at 11:31:52AM -0700, Hugh Dickins wrote: > On Wed, 1 Aug 2018, Linus Torvalds wrote: > > > > Anyway, the upshot of all this is that I think I know what the ia64 > > problem was, and John sent the patch for the ashmem case, and I'm > > going to hold off reverting that vma_is_anonymous() false-positives > > commit after all. > > I'd better send deletion of zap_pmd_range()'s VM_BUG_ON_VMA(): below > (but I've no proprietorial interest, if you prefer to do your own). Agreed. Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx> > John's patch is good, and originally I thought it was safe from that > VM_BUG_ON_VMA(), because the /dev/ashmem fd exposed to the user is > disconnected from the vm_file in the vma, and madvise(,,MADV_REMOVE) > insists on VM_SHARED. But afterwards read John's earlier mail, > drawing attention to the vfs_fallocate() in there: I may be wrong, > and I don't know if Android has THP in the config anyway, but it looks > to me like an unmap_mapping_range() from ashmem's vfs_fallocate() > could hit precisely the VM_BUG_ON_VMA(), once it's vma_is_anonymous(). > > (I'm not familiar with ashmem, and I certainly don't understand the > role of MAP_PRIVATE ashmem mappings - hole-punch's zap_pte_range() > should end up leaving any anon pages in place; but the presence of > the BUG is requiring us all to understand too much too quickly.) Hugh, do you see any reason why ashmem shouldn't have vm_ops == shmem_vm_ops? I don't understand ashmem, but I feel uncomfortable that we have this sneaky way to create an anonymous VMA. It feels wrong to me. -- Kirill A. Shutemov
