Changelog of v2:
* Change only [PATCH 2/2] and there is not any changes in [PATCH 1/2].
* Use clock_gettime(2) for getting timestamp since a system boot.
* Change parent_info's memory to dynamic allocation.
Hi,
I have been testing a cgrulesengd daemon and I noticed it fails to
change the cgroup of child occasionally. I tested it by following
configulation file:
/etc/cgrules.conf:
user01 cpuset group01/user01
% memory group01/user01
A cpuset subsystem and a memory subsystem are mounted on different
mount points, and a cgrulesengd daemon manages each subsystem.
I login this environment as a user "user01", and each susbystem's
tasks file is the following:
# cat /mnt/cgroups/cpuset/group01/user01/tasks
31801
31805
31806
#
# cat /mnt/cgroups/memory/group01/user01/tasks
31801
31805
#
# pstree -p 32105
sshd(31801)---sshd(31805)---bash(31806)
#
They should be the same, but they are different. I investigated this
problem, and I found the cause. The reason is that the process(31806)
was forked just after writing the process(31805) to a cpuset subsystem's
tasks file:
<1> The UID/GID CHANGE event of the process 31805 happens.
<2> The daemon writes "31805" to a cpuset subsystem's tasks file.
<3> The process 31806 is forked, and it appears on a cpuset subsystem's
tasks file.
<4> The daemon writes "31805" to a memory subsystem's tasks file.
<5> The process 31806 does not appears on a memory subsystem's tasks file.
For solving this problem, I propose the following sequence.
1. Store both the timestamp and the process-id when the step <4>.
2. If receiving a PROC_EVENT_FORK packet, check its parent-pid and its
timestamp.
3. If its parent-pid and the stored process-id are same and its timestamp
is older than the stored timestamp, change the cgroup of forked process.
Thanks
Ken'ichi Ohmichi
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