[CRIU] Combining pre-copy and post-copy

[Adrian Reber]

Hello Mike,

I have to come back to an old topic from September:

https://lists.openvz.org/pipermail/criu/2016-September/031672.html

I am currently trying to restore a process with pre-copy and post-copy
and it fails. The reason it fails is that the kernel claims that a page
is already there:

(03.614379) polling timeout
(03.614389) uffd: Start handling remaining pages
(03.614393) pr15740-2 Read b0e000 1 pages
(03.618349) uffd: 15740-6: uffd_copy: 0xb0e000/4096
(03.618368) Error (criu/uffd.c:682): uffd: 15740-6: UFFDIO_COPY failed: rc:-1 copy:-17

According to the pagemap it is a lazy page:

        {
            "vaddr": "0xb0e000", 
            "nr_pages": 1, 
            "flags": "PE_LAZY"
        }, 

But the kernel thinks it is already there. If I manually do an madvise MADV_DONTNEED
the uffd_copy works. So it seems somehow that the kernel thinks that the page
has already been written.

Any idea what is going on here?

		Adrian