[CRIU] failure dumping nginx in docker container

[Pavel Emelyanov]

On 06/04/2015 11:22 PM, Saied Kazemi wrote:
> I am running into the exact same CRIU failure with a mysqld server running in a container:
> 
> (00.007793) Error (proc_parse.c:404): Can't handle non-regular mapping on 26317's map 7ff7022cc000
> 
> for the following segment:
> 
> 7ff7022cc000-7ff7022ce000 rw-s 00000000 00:0a 72033                      /[aio] (deleted)
> 
> I am using CRIU 1.6 on a 3.18.0 kernel.  Below is the output of strace.  Kernel successfully opens the file:

Ah! This explains everything, please, see more details below :)

> # criu --version
> Version: 1.6
> GitID: v1.6-5-g5e1a8a2
> # criu check
> Error (cr-check.c:665): AIO remap doesn't work properly

Yup :)

> Error (cr-check.c:681): fdinfo doesn't contain the lock field
> # zcat /proc/config.gz | grep AIO
> CONFIG_AIO=y
> # CONFIG_DELL_WMI_AIO is not set
> # strace ./aio_test /proc/26317/map_files/7ff7022cc000-7ff7022ce000
> execve("./aio_test", ["./aio_test", "/proc/26317/map_files/7ff7022cc0"...], [/* 17 vars */]) = 0
> uname({sys="Linux", node="saied-cr-vm", ...}) = 0
> brk(0)                                  = 0x203d000
> brk(0x203e1c0)                          = 0x203e1c0
> arch_prctl(ARCH_SET_FS, 0x203d880)      = 0
> readlink("/proc/self/exe", "/home/saied/aio_test", 4096) = 20
> brk(0x205f1c0)                          = 0x205f1c0
> brk(0x2060000)                          = 0x2060000
> access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
> open("/proc/26317/map_files/7ff7022cc000-7ff7022ce000", O_RDONLY) = 3
> exit_group(3)                           = ?
> +++ exited with 3 +++
> 
> Any ideas?

So, there's a commit in the kernel bd9b51e7 from Al Viro which actually made files
like AIO and some more report ENXIO when trying to open() those via /proc/pid/blah
links. And this patch appeared in 3.19. Other than this, ability to remap the AIO
ring -- the crucial thing to restore AIO -- appeared with the e4a0d3e72 commit from
me also in 3.19.

When doing the AIO support I took the 3.19 kernel and implemented dump and restore
according to how the kernel worked with AIO-s that time -- reporting ENXIO on
open and letting to remap it. On 3.18 AIO C/R wouldn't work, even if we teach CRIU
to detect the ring, on restore we'll hit the problem with inability to put the
ring into proper place.

-- Pavel