[CRIU] cgroups restore issue at AWS

[Mark]

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.

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
>> 

-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openvz.org/pipermail/criu/attachments/20150825/1254c6cb/attachment.html>