On Wed, May 30, 2012 at 05:55:38PM +0400, Glauber Costa wrote: > On 05/30/2012 05:53 PM, Frederic Weisbecker wrote: > >On Wed, May 30, 2012 at 05:37:57PM +0400, Glauber Costa wrote: > >>On 05/30/2012 05:37 PM, Frederic Weisbecker wrote: > >>>Right. __mem_cgroup_get_kmem_cache() fetches the memcg of the owner > >>>and calls memcg_create_cache_enqueue() which does css_tryget(&memcg->css). > >>>After this tryget I think you're fine. And in-between you're safe against > >>>css_set removal due to rcu_read_lock(). > >>> > >>>I'm less clear with __mem_cgroup_new_kmem_page() though... > >> > >>That one does not get memcg->css but it does call mem_cgroup_get(), > >>that does prevent against the memcg structure being freed, which I > >>believe to be good enough. > > > >What if the owner calls cgroup_exit() between mem_cgroup_from_task() > >and mem_cgroup_get()? The css_set which contains the memcg gets freed. > >Also the reference on the memcg doesn't even prevent the css_set to > >be removed, does it? > It doesn't, but we don't really care. The css can go away, if the > memcg structure stays. Ah right, the memcg itself is only freed at destroy time. > The caches will outlive the memcg anyway, > since it is possible that you delete it, with some caches still > holding objects that > are not freed (they will be marked as dead). I guess I need to look at how the destroy path is handled in your patchset then. Or how you ensure that __mem_cgroup_new_kmem_page() can't race against destroy. -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>