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

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

[David Miller]

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?

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

[Shakeel Butt]

On Wed, Feb 26, 2020 at 11:07 AM David Miller <davem@davemloft.net> wrote:
>
> 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?

Currently we can potentially charge wrong cgroup. With this patch that
will be fixed but potentially half of sockets remain unaccounted. I
have a followup (incomplete) patch [1] to fix that. I will send the
next version soon.

[1] https://lore.kernel.org/linux-mm/20200222010456.40635-1-shakeelb@google.com/