netdev - Re: [PATCH v7 00/10] Request for Inclusion: per-cgroup tcp memory pressure

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Date:	Wed, 30 Nov 2011 11:11:52 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
Cc:	linux-kernel@...r.kernel.org, paul@...lmenage.org,
	lizf@...fujitsu.com, ebiederm@...ssion.com, davem@...emloft.net,
	gthelen@...gle.com, netdev@...r.kernel.org, linux-mm@...ck.org,
	kirill@...temov.name, avagin@...allels.com, devel@...nvz.org,
	eric.dumazet@...il.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v7 00/10] Request for Inclusion: per-cgroup tcp memory
 pressure

On Tue, 29 Nov 2011 21:56:51 -0200
Glauber Costa <glommer@...allels.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 ?

Thanks,
-Kame



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