On Mon, Jun 25, 2018 at 05:06:23PM -0700, Yang Shi wrote: > By looking this deeper, we may not be able to cover all the unmapping range > for VM_DEAD, for example, if the start addr is in the middle of a vma. We > can't set VM_DEAD to that vma since that would trigger SIGSEGV for still > mapped area. > > splitting can't be done with read mmap_sem held, so maybe just set VM_DEAD > to non-overlapped vmas. Access to overlapped vmas (first and last) will > still have undefined behavior. Acquire mmap_sem for writing, split, mark VM_DEAD, drop mmap_sem. Acquire mmap_sem for reading, madv_free drop mmap_sem. Acquire mmap_sem for writing, free everything left, drop mmap_sem. ? Sure, you acquire the lock 3 times, but both write instances should be 'short', and I suppose you can do a demote between 1 and 2 if you care.
