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

[Pavel Emelyanov]

On 11/27/2015 05:51 PM, Adrian Reber wrote:
> 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

Hm... Do you use the recent head? I've introduced this bug about 2-3 weeks
ago and have fixed it some days later :)

> 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"
>                 }, 

This is mm.img part, while page-read engine deals with pagemap-xxx.img files where
triplets of [start len in_parent] sit.

> 
> 
> 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
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