Re: [PATCH 3/3] mm/memcg: iteration skip memcgs not yet fully initialized
From: Michal Hocko <hidden>
Date: 2014-01-15 08:21:42
Also in:
lkml
On Mon 13-01-14 17:54:04, Hugh Dickins wrote:
It is surprising that the mem_cgroup iterator can return memcgs which have not yet been fully initialized. By accident (or trial and error?) this appears not to present an actual problem; but it may be better to prevent such surprises, by skipping memcgs not yet online. Signed-off-by: Hugh Dickins <hughd@google.com>
This makes a perfect sense now after Tejun pointed out that I was wrong assuming css_online is called before cgroup is made visible. Acked-by: Michal Hocko <redacted>
quoted hunk ↗ jump to hunk
--- Decide for yourself whether to take this or not. I spent quite a while digging into a mysterious "trying to register non-static key" issue from lockdep, which originated from the iterator returning a vmalloc'ed memcg a moment before the res_counter_init()s had done their spin_lock_init()s. But the backtrace was an odd one of our own mis-devising, not a charge or reclaim or stats trace, so probably it's never been a problem for vanilla. mm/memcontrol.c | 6 ++---- 1 file changed, 2 insertions(+), 4 deletions(-)--- mmotm/mm/memcontrol.c 2014-01-10 18:25:02.236448954 -0800 +++ linux/mm/memcontrol.c 2014-01-12 22:21:10.700570471 -0800@@ -1119,10 +1119,8 @@ skip_node: * protected by css_get and the tree walk is rcu safe. */ if (next_css) { - struct mem_cgroup *mem = mem_cgroup_from_css(next_css); - - if (css_tryget(&mem->css)) - return mem; + if ((next_css->flags & CSS_ONLINE) && css_tryget(next_css)) + return mem_cgroup_from_css(next_css); else { prev_css = next_css; goto skip_node;
-- Michal Hocko SUSE Labs -- 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: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>