Re: [PATCH] cgroup_pids: add fork limit

From: Aleksa Sarai
Date: Sun Nov 15 2015 - 08:36:50 EST

>> If so, could you share little more insight on how that time measure
>> outside of the cpu's cgroup cycles? Just so that its helpful to wider
>> audience.
> Well, there are a number of things that I can think of that the kernel does
> on behalf of processes that can consume processor time that isn't trivial to
> account:
> * Updating timers on behalf of userspace processes (itimers or similar).
> * Sending certain kernel generated signals to processes (that is, stuff
> generated by the kernel like SIGFPE, SIGSEGV, and so forth).
> * Queuing events from dnotify/inotify/fanotify.
> * TLB misses, page faults, and swapping.
> * Setting up new processes prior to them actually running.
> * Scheduling.
> All of these are things that fork-bombs can and (other than TLB misses) do
> exploit to bring a system down, and the cpu cgroup is by no means a magic
> bullet to handle this.

I feel like these are backed by different resources, and we should
work on limiting those *at the source* in the context of a controller
rather than just patching up the symptoms (too many forks causing
issues), because these are symptoms of a larger issue IMO.

Aleksa Sarai (cyphar)
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