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

[Andrew Vagin]

Pavel, I have modified your test and criu restore failed. It is always bad, all
errors have to be reported on dump.

[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
>