On Tue, 21 Jan 2014 11:45:43 +0100 Michal Hocko <mhocko@xxxxxxx> wrote: > 19f39402864e (memcg: simplify mem_cgroup_iter) has reorganized > mem_cgroup_iter code in order to simplify it. A part of that change was > dropping an optimization which didn't call css_tryget on the root of > the walked tree. The patch however didn't change the css_put part in > mem_cgroup_iter which excludes root. > This wasn't an issue at the time because __mem_cgroup_iter_next bailed > out for root early without taking a reference as cgroup iterators > (css_next_descendant_pre) didn't visit root themselves. > > Nevertheless cgroup iterators have been reworked to visit root by > bd8815a6d802 (cgroup: make css_for_each_descendant() and friends include > the origin css in the iteration) when the root bypass have been dropped > in __mem_cgroup_iter_next. This means that css_put is not called for > root and so css along with mem_cgroup and other cgroup internal object > tied by css lifetime are never freed. > > Fix the issue by reintroducing root check in __mem_cgroup_iter_next > and do not take css reference for it. > > This reference counting magic protects us also from another issue, an > endless loop reported by Hugh Dickins when reclaim races with root > removal and css_tryget called by iterator internally would fail. There > would be no other nodes to visit so __mem_cgroup_iter_next would return > NULL and mem_cgroup_iter would interpret it as "start looping from root > again" and so mem_cgroup_iter would loop forever internally. I grabbed these two patches but I will sit on them for a week or so, pending review-n-test. > Cc: stable@xxxxxxxxxxxxxxx # mem_leak part 3.12+ What does this mean? -- 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>