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.
My understanding was that !online cgroups are not visible for the iterator. it is css_online that has to be called before they are made visible. Tejun? > Signed-off-by: Hugh Dickins <[email protected]> > --- > 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 from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
