Re: CLONE_INTO_CGROUP probably needs to call controller attach handlers
From: Waiman Long
Date: Tue Mar 28 2023 - 22:49:41 EST
On 3/28/23 21:30, Waiman Long wrote:
On 3/28/23 11:39, Christian Brauner wrote:
Hey,
Giuseppe reported that the the affinity mask isn't updated when a
process is spawned directly into the target cgroup via
CLONE_INTO_CGROUP. However, migrating a process will cause the affinity
mask to be updated (see the repro at [1].
I took a quick look and the issue seems to be that we don't call the
various attach handlers during CLONE_INTO_CGROUP whereas we do for
migration. So the solution seems to roughly be that we need to call the
various attach handlers during CLONE_INTO_CGROUP as well when the
parent's cgroups is different from the child cgroup. I think we need to
call all of them, can, cancel and attach.
The plumbing here might be a bit intricate since the arguments that the
fork handlers take are different from the attach handlers.
Christian
[1]: https://paste.centos.org/view/f434fa1a
I saw that the current cgroup code already have the can_fork, fork and
cancel_fork callbacks. Unfortunately such callbacks are not defined
for cpuset yet. That is why the cpu affinity isn't correctly updated.
I can post a patch to add those callback functions to cpuset which
should then able to correctly address this issue.
Looking further into this issue, I am thinking that forking into a
cgroup should be equivalent to write the child pid into the
"cgroup.threads" file of the target cgroup. By taking this route, all
the existing can_attach, attach and cancel_attach methods can be used. I
believe the original fork method is for the limited use case of forking
into the same cgroup. So right now, only the pids controller has the
fork methods. Otherwise, we will have to modify a number of different
controllers to add the necessary fork methods. They will be somewhat
similar to the existing attach methods and so it will be a lot of
duplication. What do you think about this idea?
Cheers,
Longman