On Mon, Apr 22, 2019 at 02:29:16PM -0700, Michel Lespinasse wrote: > The proposed spf mechanism only handles anon vmas. Is there a > fundamental reason why it couldn't handle mapped files too ? > My understanding is that the mechanism of verifying the vma after > taking back the ptl at the end of the fault would work there too ? > The file has to stay referenced during the fault, but holding the vma's > refcount could be made to cover that ? the vm_file refcount would have > to be released in __free_vma() instead of remove_vma; I'm not quite sure > if that has more implications than I realize ?
IIRC (and I really don't remember all that much) the trickiest bit was vs unmount. Since files can stay open past the 'expected' duration, umount could be delayed. But yes, I think I had a version that did all that just 'fine'. Like mentioned, I didn't keep the refcount because it sucked just as hard as the mmap_sem contention, but the SRCU callback did the fput() just fine (esp. now that we have delayed_fput).
