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From "Adar Dembo (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (YARN-799) CgroupsLCEResourcesHandler tries to write to cgroup.procs
Date Thu, 13 Jun 2013 20:47:20 GMT

    [ https://issues.apache.org/jira/browse/YARN-799?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13682698#comment-13682698
] 

Adar Dembo commented on YARN-799:
---------------------------------

Thread group IDs should be written to /cgroup.procs while individual thread IDs are written
to /tasks. Effectively this means that /cgroup.procs can be used to atomically move entire
processes to a cgroup, while /tasks requires cgroup movement occur thread by thread, an inherently
racy operation (i.e. a new thread is created during the move will be left behind in the old
cgroup unless the move is retried). That makes /cgroup.procs more attractive for cgroup migration.
Once threads are in the new cgroup, it doesn't matter how they got there: if they fork, their
children will be in the new cgroup too.

However, /cgroup.procs has some issues:
# As identified in the original bug report, /cgroup.procs wasn't always writable, so we'd
need to fall back to /tasks when /cgroup.procs is read-only.
# On all SLES 11 kernels I've tested (including the upcoming SLES 11 SP3), it's trivial to
crash the kernel via /cgroup.procs.
                
> CgroupsLCEResourcesHandler tries to write to cgroup.procs
> ---------------------------------------------------------
>
>                 Key: YARN-799
>                 URL: https://issues.apache.org/jira/browse/YARN-799
>             Project: Hadoop YARN
>          Issue Type: Bug
>          Components: nodemanager
>    Affects Versions: 2.0.4-alpha, 2.0.5-alpha
>            Reporter: Chris Riccomini
>
> The implementation of
> bq. ./hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/java/org/apache/hadoop/yarn/server/nodemanager/util/CgroupsLCEResourcesHandler.java
> Tells the container-executor to write PIDs to cgroup.procs:
> {code}
>   public String getResourcesOption(ContainerId containerId) {
>     String containerName = containerId.toString();
>     StringBuilder sb = new StringBuilder("cgroups=");
>     if (isCpuWeightEnabled()) {
>       sb.append(pathForCgroup(CONTROLLER_CPU, containerName) + "/cgroup.procs");
>       sb.append(",");
>     }
>     if (sb.charAt(sb.length() - 1) == ',') {
>       sb.deleteCharAt(sb.length() - 1);
>     } 
>     return sb.toString();
>   }
> {code}
> Apparently, this file has not always been writeable:
> https://patchwork.kernel.org/patch/116146/
> http://lkml.indiana.edu/hypermail/linux/kernel/1004.1/00536.html
> https://lists.linux-foundation.org/pipermail/containers/2009-July/019679.html
> The RHEL version of the Linux kernel that I'm using has a CGroup module that has a non-writeable
cgroup.procs file.
> {quote}
> $ uname -a
> Linux criccomi-ld 2.6.32-131.4.1.el6.x86_64 #1 SMP Fri Jun 10 10:54:26 EDT 2011 x86_64
x86_64 x86_64 GNU/Linux
> {quote}
> As a result, when the container-executor tries to run, it fails with this error message:
> bq.    fprintf(LOGFILE, "Failed to write pid %s (%d) to file %s - %s\n",
> This is because the executor is given a resource by the CgroupsLCEResourcesHandler that
includes cgroup.procs, which is non-writeable:
> {quote}
> $ pwd 
> /cgroup/cpu/hadoop-yarn/container_1370986842149_0001_01_000001
> $ ls -l
> total 0
> -r--r--r-- 1 criccomi eng 0 Jun 11 14:43 cgroup.procs
> -rw-r--r-- 1 criccomi eng 0 Jun 11 14:43 cpu.rt_period_us
> -rw-r--r-- 1 criccomi eng 0 Jun 11 14:43 cpu.rt_runtime_us
> -rw-r--r-- 1 criccomi eng 0 Jun 11 14:43 cpu.shares
> -rw-r--r-- 1 criccomi eng 0 Jun 11 14:43 notify_on_release
> -rw-r--r-- 1 criccomi eng 0 Jun 11 14:43 tasks
> {quote}
> I patched CgroupsLCEResourcesHandler to use /tasks instead of /cgroup.procs, and this
appears to have fixed the problem.
> I can think of several potential resolutions to this ticket:
> 1. Ignore the problem, and make people patch YARN when they hit this issue.
> 2. Write to /tasks instead of /cgroup.procs for everyone
> 3. Check permissioning on /cgroup.procs prior to writing to it, and fall back to /tasks.
> 4. Add a config to yarn-site that lets admins specify which file to write to.
> Thoughts?

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