[CRIU] [PATCH 0/2] support restoring ghost files on readonly mounts

[Pavel Tikhomirov]

On 09/12/2018 02:54 AM, Andrew Vagin wrote:
> Pavel, I have modified your test and criu restore failed.

Thanks, the error is not expected here. I didn't took into account the 
mount remap, which breaks mnt_is_overmounted helper.

> It is always bad, all errors have to be reported on dump.

Will try to add a check on dump for exeptions (overmounted ghosts on 
readonly mounts).

> 
> [root at fc24 criu]# git diff
> diff --git a/test/zdtm/static/ghost_on_rofs.c b/test/zdtm/static/ghost_on_rofs.c
> index 6362e8334..32966f910 100644
> --- a/test/zdtm/static/ghost_on_rofs.c
> +++ b/test/zdtm/static/ghost_on_rofs.c
> @@ -131,6 +131,10 @@ int main(int argc, char **argv)
>                  pr_perror("mount");
>                  return 1;
>          }
> +       if (mount("ro_mount", dirname, "tmpfs", 0, NULL)) {
> +               pr_perror("mount");
> +               return 1;
> +       }
>   
>          test_daemon();
>          test_waitsig();
> @@ -158,6 +162,10 @@ int main(int argc, char **argv)
>          close(fd);
>          close(fd_bind);
>   
> +       if (umount(dirname)) {
> +               pr_perror("Unable to umount %s", ro_mount);
> +               return 1;
> +       }
>          if (umount(ro_bind_mount)) {
>                  pr_perror("Unable to umount %s", ro_bind_mount);
>                  return 1;
> 
> 
> [root at fc24 criu]# python test/zdtm.py run -t zdtm/static/ghost_on_rofs --sbs
> === Run 1/1 ================ zdtm/static/ghost_on_rofs
> ===================== Run zdtm/static/ghost_on_rofs in ns ======================
>   DEP       ghost_on_rofs.d
>   CC        ghost_on_rofs.o
>   LINK      ghost_on_rofs
> Start test
> Test is SUID
> ./ghost_on_rofs --pidfile=ghost_on_rofs.pid --outfile=ghost_on_rofs.out --dirname=ghost_on_rofs.test
> Pause at pre-dump. Press Enter to continue.
> Run criu dump
> files stat: fs/file-max 400660, fs/nr_open 1048576
> rlimit: RLIMIT_NOFILE unlimited for self
> Loaded kdat cache from /run/criu.kdat
> 
> Pause at pre-restore. Press Enter to continue.Run criu restore
> files stat: fs/file-max 400660, fs/nr_open 1048576
> rlimit: RLIMIT_NOFILE unlimited for self
> Loaded kdat cache from /run/criu.kdat
> =[log]=> dump/zdtm/static/ghost_on_rofs/70/1/restore.log
> ------------------------ grep Error ------------------------
> (00.384819) pie: 4: vdso: Remap rt-vdso 0x2b000 -> 0x7ffc4c4ff000
> (00.384832) pie: 4: vdso: Remap rt-vvar 0x28000 -> 0x7ffc4c4fc000
> (00.384882) pie: 4: Restoring scheduler params 0.0.0
> (00.384927) pie: 4: 4: Restored
> (00.385068)      1: mnt: Switched to mntns 12:0/n(00.385104)      1: Error (criu/mount.c:3702): mnt: Failed to restore 195:/tmp/.criu.mntns.d8M3QA/12-0000000000/zdtm/static/ghost_on_rofs.test/ro_mount mount flags 300001: No such file or directory
> (00.385163)      1: Error (criu/mount.c:3764): mnt: Can't wait or bad status: errno=0, status=256
> (00.403322) Error (criu/cr-restore.c:1428): 97 exited, status=1
> (00.403378) Warn  (criu/cr-restore.c:2294): Unable to wait 97: No child processes
> (00.403390) mnt: Switching to new ns to clean ghosts
> (00.403490) Unlink remap zdtm/static/ghost_on_rofs.test/ghost_file.cr.1.ghost
> (00.403543) Unlink remap zdtm/static/ghost_on_rofs.test/ghost_file_bind.cr.2.ghost
> (00.419163) Error (criu/cr-restore.c:2308): Restoring FAILED.
> ------------------------ ERROR OVER ------------------------
> ############# Test zdtm/static/ghost_on_rofs FAIL at CRIU restore ##############
> ##################################### FAIL #####################################
> 
> 
> On Tue, Sep 11, 2018 at 06:53:29PM +0300, Pavel Tikhomirov wrote:
>> We have a problem restoring ghost-files on readonly mounts:
>>
>> Failed to resume the CT: PRL_ERR_VZCTL_OPERATION_FAILED (Details: (04.800253)      1: Error (criu/files-reg.c:381): Can't create ghost regfile: Read-only file system
>> (04.916178) Error (criu/files-reg.c:868): Couldn't unlink remap 17 lib/x86_64-linux-gnu/libm-2.24.so.dpkg-new.cr.22.ghost: Read-only file system
>> (04.916190) Error (criu/files-reg.c:868): Couldn't unlink remap 17 lib/x86_64-linux-gnu/libm-2.24.so.dpkg-new.cr.22.ghost: No such file or directory
>> (04.945551) Error (criu/cr-restore.c:2340): Restoring FAILED.
>>
>> See description of the first patch for explanation of the fix.
>>
>> Just to note: I thought about two other possible ways of making these
>> work: Find a writable bind-mount - but there can be no such a thing, see
>> the test-patch. Remount the mount writable just before creating ghosts
>> and remount it back after it - we operate ghosts in three places
>> (create, give it the right name, remove) so these approach brings a lot
>> of extra remounts and is hardly a good way.
>>
>> https://jira.sw.ru/browse/PSBM-82991
>>
>> Pavel Tikhomirov (2):
>>    mount: delay restoring readonly mount flag untill all files ready
>>    zdtm: ghost on readonly fs
>>
>>   criu/cr-restore.c                   |   2 +
>>   criu/include/mount.h                |   2 +
>>   criu/mount.c                        | 112 ++++++++++++++++-
>>   test/zdtm/static/Makefile           |   1 +
>>   test/zdtm/static/ghost_on_rofs.c    | 179 ++++++++++++++++++++++++++++
>>   test/zdtm/static/ghost_on_rofs.desc |   1 +
>>   6 files changed, 295 insertions(+), 2 deletions(-)
>>   create mode 100644 test/zdtm/static/ghost_on_rofs.c
>>   create mode 100644 test/zdtm/static/ghost_on_rofs.desc
>>
>> -- 
>> 2.17.1
>>

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.