On 04/02/2013 12:34 PM, Li Zefan wrote: > 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. > Yes, but I tend to test that with manually introduced error codes. For what is worth, I just did it. And indeed, by ignoring kmemcg initialization and failing with ENOMEM here triggers a bug. Your patch fixes it. I tested both failing all non-root, and letting the first succeed and failing the second if the parent is use_hierarchy. Both cases have a bug initially that you fix. If that is allowed to proceed, kmemcg initialization and teardown works as expected. >> 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. > Yes, this is possible, -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>