[CRIU] cgroups restore issue at AWS

[Hui Kang]

On Tue, Aug 25, 2015 at 11:40 AM, Mark <fl0yd at me.com> wrote:
> I'm using Docker 1.9 experimental, the one that has your network changes in
> it from Boucher's branch.
>
> I've tried CG_MODE_SOFT and FULL and in both cases the ffclose(f) still
> returns Invalid Argument.

I remember I used full mode and then manually run "echo 0 >
/sys/fs/cgroup/cpuset/docker/cpuset.cpus" and "echo 0 >
/sys/fs/cgroup/cpuset/docker/cpuset.mems"

Then the restore will success. Have you tried this?

- Hui

>
> Mark
>
> On Aug 25, 2015, at 10:36 AM, Hui Kang <hkang.sunysb at gmail.com> wrote:
>
> Hi, Mark
> I think the failure is caused by criu restoring the root directory of group.
>
> Which branch of docker you used to restore a container? You probably
> need to set manage-cgroup=full.
>
> - Hui
>
> On Tue, Aug 25, 2015 at 5:44 AM, Pavel Emelyanov <xemul at parallels.com>
> wrote:
>
> On 08/22/2015 01:39 AM, Mark wrote:
>
> Hi,
>
> We're seeing some issues doing docker-based restores on AWS machines.  On
> the first try the restore.log shows the following output:
>  (00.000551) cg: Preparing cgroups yard (cgroups restore mode 0x4)
>  (00.000607) cg: Opening .criu.cgyard.aRmYI0 as cg yard
>  (00.000617) cg:         Making controller dir .criu.cgyard.aRmYI0/cpuset
> (cpuset)
>  (00.000691) cg: Created cgroup dir
> cpuset/system.slice/docker-f00d0fe34bcc352377f4750f99fc4a649bd14db65fc15639df35043c62f7733a.scope
>  (00.000733) Error (cgroup.c:978): cg: Failed closing
> cpuset/system.slice/docker-f
> 00d0fe34bcc352377f4750f99fc4a649bd14db65fc15639df35043c62f7733a.scope/cpuset.cpus:
> Invalid argument
>  (00.000737) Error (cgroup.c:1083): cg: Restoring special cpuset props
> failed!
>
>
> Failure to close the file is actually because fprintf fails.
>
> On the 2nd try the restore works because it skips the attempt:
>
>  (00.000785) cg: Preparing cgroups yard (cgroups restore mode 0x4)
>  (00.000840) cg: Opening .criu.cgyard.BQ2bKQ as cg yard
>  (00.000850) cg:     Making controller dir .criu.cgyard.BQ2bKQ/cpuset
> (cpuset)
>  (00.000877) cg: Determined cgroup dir
> cpuset/system.slice/docker-404a13eab68e35753ee2c66f636aa727aa2c9a7723671d25cc9ffb0ede574178.scope
> already exist
>  (00.000880) cg: Skip restoring properties on cgroup dir
> cpuset/system.slice/docker-404a13eab68e35753ee2c66f636aa727aa2c9a7723671d25cc9ffb0ede574178.scope
>
>
> Well, yes, this is because the directory was created on first restore.
>
> It appears to be a timing issue on the fclose(f) call in cgroups.c.  I've
> tried using CG_MODE_SOFT and CG_MODE_FULL and neither have an affect, the
> 1st attempt fails and the 2nd succeeds.
>
> To workaround the issue, we've created a fork with these changes and the
> issue hasn't recurred.  In fact there hasn't even been a single "Failed to
> flush..." message printed in the logs, so it seems to be a matter of split
> second timing that the for loop allows enough time for the handle to flush.
>
> diff --git a/cgroup.c b/cgroup.c
> index a4e0146..9495206 100644
> --- a/cgroup.c
> +++ b/cgroup.c
> @@ -950,6 +950,8 @@ static int restore_cgroup_prop(const CgroupPropEntry *
> cg_prop_entry_p,
> {
>        FILE *f;
>        int cg;
> +       int flushcounter=0;
> +       int maxtries=500;
>
>        if (!cg_prop_entry_p->value) {
>                pr_err("cg_prop_entry->value was empty when should have had a
> value");
> @@ -974,9 +976,26 @@ static int restore_cgroup_prop(const CgroupPropEntry *
> cg_prop_entry_p,
>                return -1;
>        }
>
> +       /* The fclose() below was failing intermittently with EINVAL at
> AWS*/
> +       /* So we try fflush() in a loop until it succeeds or we've */
> +       /* tried it a bunch. */
> +       for (;;) {
> +               flushcounter++;
> +               if (fflush(f) == 0) {
> +                       break;
> +               }
> +               if (flushcounter > maxtries) {
> +                       pr_perror("Max fflush() tries %d exceeded.  Moving
> along anyway.\n",maxtries);
> +                       break;
> +               }
> +               if (fflush(f) != 0) {
> +                 pr_perror("Failed to flush %s [%d/%d]\n", path,
> flushcounter,maxtries);
> +               }
> +       }
> +
>
>
> Does this help?!
>
>        if (fclose(f) != 0) {
> -               pr_perror("Failed closing %s", path);
> -               return -1;
> +         pr_perror("Failed closing %s\n",path);
> +         return -1;
>        }
>
> Can anyone reproduce the issue of offer a suggestion on how we should
> proceed?
>
>
> Hui (in Cc) sees similar in his experiments.
>
> -- Pavel
>
>