Messages in this thread | | | Date | Tue, 2 Apr 2013 16:34:33 +0800 | From | Li Zefan <> | Subject | Re: [PATCH] memcg: don't do cleanup manually if mem_cgroup_css_online() fails |
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On 2013/4/2 16:07, Glauber Costa wrote: > On 04/02/2013 12:03 PM, Li Zefan wrote: >> On 2013/4/2 15:35, Li Zefan wrote: >>> If memcg_init_kmem() returns -errno when a memcg is being created, >>> mem_cgroup_css_online() will decrement memcg and its parent's refcnt, >> >>> (but strangely there's no mem_cgroup_put() for mem_cgroup_get() called >>> in memcg_propagate_kmem()). >> >> The comment in memcg_propagate_kmem() suggests it knows mem_cgroup_css_free() >> will be called in failure, while mem_cgroup_css_online() doesn't know. >> > This is a bit suspicious. At first your analysis seems fair, but I've > extensively tested memcg teardown process with kmemcg (and even > uncovered some bugs at that), and it works when and how expected. >
Because this bug is in a failure path, and seems the only way to get into this path is -ENOMEM.
> Also, note that this teardown code long predates kmemcg. >
Maybe this bug was introduced when ss->create() was changed to ss->css_alloc() and ss->css_online(), and before that change ss->destroy() won't be called if ss->create() failed.
> I am not saying your are wrong - on the contrary, you seem to be right, > but I think this one needs to be handled with extra care. I will run > some tests, take a look, and get back to you. >
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