[CRIU] cgroups restore issue at AWS

[Mark]

I haven't tried that.  I was trying to use the native features within CRIU to do this.  I'm not particularly interested in another workaround since i have one, I'm more interested in trying to understand the root cause.

Mark

> On Aug 25, 2015, at 10:42 AM, Hui Kang <hkang.sunysb at gmail.com> wrote:
> 
> 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
>> 
>> 

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