From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx195.postini.com [74.125.245.195]) by kanga.kvack.org (Postfix) with SMTP id DFEF06B0072 for ; Mon, 26 Nov 2012 13:48:12 -0500 (EST) From: Michal Hocko Subject: [patch v2 2/6] memcg: keep prev's css alive for the whole mem_cgroup_iter Date: Mon, 26 Nov 2012 19:47:47 +0100 Message-Id: <1353955671-14385-3-git-send-email-mhocko@suse.cz> In-Reply-To: <1353955671-14385-1-git-send-email-mhocko@suse.cz> References: <1353955671-14385-1-git-send-email-mhocko@suse.cz> Sender: owner-linux-mm@kvack.org List-ID: To: linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki , Johannes Weiner , Ying Han , Tejun Heo , Glauber Costa , Li Zefan css reference counting keeps the cgroup alive even though it has been already removed. mem_cgroup_iter relies on this fact and takes a reference to the returned group. The reference is then released on the next iteration or mem_cgroup_iter_break. mem_cgroup_iter currently releases the reference right after it gets the last css_id. This is correct because neither prev's memcg nor cgroup are accessed after then. This will change in the next patch so we need to hold the group alive a bit longer so let's move the css_put at the end of the function. Signed-off-by: Michal Hocko --- mm/memcontrol.c | 13 +++++++------ 1 file changed, 7 insertions(+), 6 deletions(-) diff --git a/mm/memcontrol.c b/mm/memcontrol.c index 0e52ec9..1f5528d 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c @@ -1077,12 +1077,9 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, if (prev && !reclaim) id = css_id(&prev->css); - if (prev && prev != root) - css_put(&prev->css); - if (!root->use_hierarchy && root != root_mem_cgroup) { if (prev) - return NULL; + goto out_css_put; return root; } @@ -1100,7 +1097,7 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, spin_lock(&iter->iter_lock); if (prev && reclaim->generation != iter->generation) { spin_unlock(&iter->iter_lock); - return NULL; + goto out_css_put; } id = iter->position; } @@ -1124,8 +1121,12 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root, } if (prev && !css) - return NULL; + goto out_css_put; } +out_css_put: + if (prev && prev != root) + css_put(&prev->css); + return memcg; } -- 1.7.10.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org