On 08/29/2017 05:34 PM, Peter Zijlstra wrote: > On Tue, Aug 29, 2017 at 09:59:30AM +0200, Laurent Dufour wrote: >> On 27/08/2017 02:18, Kirill A. Shutemov wrote: >>>> + >>>> + if (unlikely(!vma->anon_vma)) >>>> + goto unlock; >>> It deserves a comment. >> You're right I'll add it in the next version. >> For the record, the root cause is that __anon_vma_prepare() requires the >> mmap_sem to be held because vm_next and vm_prev must be safe. > But should that test not be: > > if (unlikely(vma_is_anonymous(vma) && !vma->anon_vma)) > goto unlock;
This makes more sense. We are backing off from speculative path because struct anon_vma has not been created for this anonymous vma and we cannot do that without holding mmap_sem. This should have nothing to do with vma->vm_ops availability.
