Re: [PATCH v2] cgroup: memcg: net: do not associate sock with unrelated cgroup

[Roman Gushchin]

On Fri, Feb 14, 2020 at 02:24:15PM -0800, Shakeel Butt wrote:
> 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.
> 
> Fixes: 2d7580738345 ("mm: memcontrol: consolidate cgroup socket tracking")
> Fixes: d979a39d7242 ("cgroup: duplicate cgroup reference when cloning sockets")
> Signed-off-by: Shakeel Butt <shakeelb@xxxxxxxxxx>
> ---
> 
> Changes since v1:
> - Fix cgroup_sk_alloc() too.
> 
>  kernel/cgroup/cgroup.c | 4 ++++
>  mm/memcontrol.c        | 4 ++++
>  2 files changed, 8 insertions(+)
> 
> diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
> index 9a8a5ded3c48..46e5f5518fba 100644
> --- a/kernel/cgroup/cgroup.c
> +++ b/kernel/cgroup/cgroup.c
> @@ -6449,6 +6449,10 @@ void cgroup_sk_alloc(struct sock_cgroup_data *skcd)
>  		return;
>  	}
>  
> +	/* Do not associate the sock with unrelated interrupted task's memcg. */
                                                                       ^^^^^
								       cgroup?
> +	if (in_interrupt())
> +		return;
> +
>  	rcu_read_lock();
>  
>  	while (true) {
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index 63bb6a2aab81..f500da82bfe8 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -6697,6 +6697,10 @@ void mem_cgroup_sk_alloc(struct sock *sk)
>  		return;
>  	}

Can you, please, include the stacktrace into the commit log?
Except a minor typo (see above),
Reviewed-by: Roman Gushchin <guro@xxxxxx>

A really good catch.

Thank you!