| Re: [PATCH v7 00/10] Request for Inclusion: per-cgroup tcp memory pressure [message #44367 is a reply to message #44324] |
Fri, 02 December 2011 18:04   |
Glauber Costa
Messages: 916
Registered: October 2011
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Senior Member |
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On 11/30/2011 12:11 AM, KAMEZAWA Hiroyuki wrote:
> On Tue, 29 Nov 2011 21:56:51 -0200
> Glauber Costa<glommer@parallels.com> wrote:
>
>> Hi,
>>
>> This patchset implements per-cgroup tcp memory pressure controls. It did not change
>> significantly since last submission: rather, it just merges the comments Kame had.
>> Most of them are style-related and/or Documentation, but there are two real bugs he
>> managed to spot (thanks)
>>
>> Please let me know if there is anything else I should address.
>>
>
> After reading all codes again, I feel some strange. Could you clarify ?
>
> Here.
> ==
> +void sock_update_memcg(struct sock *sk)
> +{
> + /* right now a socket spends its whole life in the same cgroup */
> + if (sk->sk_cgrp) {
> + WARN_ON(1);
> + return;
> + }
> + if (static_branch(&memcg_socket_limit_enabled)) {
> + struct mem_cgroup *memcg;
> +
> + BUG_ON(!sk->sk_prot->proto_cgroup);
> +
> + rcu_read_lock();
> + memcg = mem_cgroup_from_task(current);
> + if (!mem_cgroup_is_root(memcg))
> + sk->sk_cgrp = sk->sk_prot->proto_cgroup(memcg);
> + rcu_read_unlock();
> ==
>
> sk->sk_cgrp is set to a memcg without any reference count.
>
> Then, no check for preventing rmdir() and freeing memcgroup.
>
> Is there some css_get() or mem_cgroup_get() somewhere ?
>
There were a css_get in the first version of this patchset. It was
removed, however, because it was deemed anti-intuitive to prevent rmdir,
since we can't know which sockets are blocking it, or do anything about
it. Or did I misunderstand something ?
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