[CRIU] More uffd related questions (Error (page-read.c:128): Missing 7fff408d8000 in parent pagemap)

[Adrian Reber]

In addition to the pages requested via uffd I am now copying the not
requested pages into the process using uffd.

The first part is waiting for requests from uffd and tracking which pages
have been transferred and once this part has finished I am switching to
'copy-the-rest' mode. I am going through my list of pages and I am now
copying each page into the process using uffd.

This works for the first two pages in my list but seeking to the third page
fails with in seek_pagemap_page():

(05.009260) Error (page-read.c:128): Missing 7fff408d8000 in parent pagemap, current iov: base=7fff408d9000,len=12288

Reading the page then also fails:

(05.009264) pr11 Read 7fff408d8000 1 pages
(05.009266) Error (page-read.c:152): Page read err 7fff408d9000:3 vs 7fff408d8000:1
(05.009267) Error (page-read.c:153): BUG at page-read.c:153
Aborted

Looking at crit's output I cannot detect anything special regarding this
pages:

                {
                    "start": "0x7fff408ba000", 
                    "end": "0x7fff408dc000", 
                    "pgoff": 0, 
                    "shmid": 0, 
                    "prot": "PROT_READ | PROT_WRITE", 
                    "flags": "MAP_PRIVATE | MAP_ANON | MAP_GROWSDOWN", 
                    "status": "0x201", 
                    "fd": -1, 
                    "fdflags": "0x0"
                }, 



It is probably difficult to answer as I am doing all kinds of strange
operations with pages for the uffd implementation, but maybe someone has
an idea what is going wrong and why. Thanks.

		Adrian