Re: [PATCH v3] cgroup: memcg: net: do not associate sock with unrelated cgroup

[David Miller <davem@davemloft.net>]

From: Shakeel Butt <shakeelb@google.com>
Date: Thu, 20 Feb 2020 17:46:04 -0800

> We are testing network memory accounting in our setup and noticed
> inconsistent network memory usage and often unrelated cgroups network
> usage correlates with testing workload. On further inspection, it
> seems like mem_cgroup_sk_alloc() and cgroup_sk_alloc() are broken in
> IRQ context specially for cgroup v1.
> 
> mem_cgroup_sk_alloc() and cgroup_sk_alloc() can be called in IRQ context
> and kind of assumes that this can only happen from sk_clone_lock()
> and the source sock object has already associated cgroup. However in
> cgroup v1, where network memory accounting is opt-in, the source sock
> can be unassociated with any cgroup and the new cloned sock can get
> associated with unrelated interrupted cgroup.
> 
> Cgroup v2 can also suffer if the source sock object was created by
> process in the root cgroup or if sk_alloc() is called in IRQ context.
> The fix is to just do nothing in interrupt.
> 
> WARNING: Please note that about half of the TCP sockets are allocated
> from the IRQ context, so, memory used by such sockets will not be
> accouted by the memcg.

Then if we do this then we have to have some kind of subsequent change
to attach these sockets to the correct cgroup, right?