From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Hocko Subject: Re: [RFC PATCH] mm: memcg: fix css double put in mem_cgroup_iter Date: Thu, 27 Jul 2017 08:53:15 +0200 Message-ID: <20170727065314.GC20970@dhcp22.suse.cz> References: <20170726130742.5976-1-wenwei.tww@gmail.com> <20170726134451.GR2981@dhcp22.suse.cz> Mime-Version: 1.0 Return-path: Content-Disposition: inline In-Reply-To: Sender: cgroups-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Wenwei Tao Cc: Johannes Weiner , Balbir Singh , kamezawa.hiroyu-+CUm20s59erQFUHtdCDX3A@public.gmane.org, yuwang.yuwang-gPhfCIXyaqCqndwCJWfcng@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Wenwei Tao On Thu 27-07-17 11:30:50, Wenwei Tao wrote: > 2017-07-26 21:44 GMT+08:00 Michal Hocko : > > On Wed 26-07-17 21:07:42, Wenwei Tao wrote: [...] > >> I think there is a css double put in mem_cgroup_iter. Under reclaim, > >> we call mem_cgroup_iter the first time with prev == NULL, and we get > >> last_visited memcg from per zone's reclaim_iter then call __mem_cgroup_iter_next > >> try to get next alive memcg, __mem_cgroup_iter_next could return NULL > >> if last_visited is already the last one so we put the last_visited's > >> memcg css and continue to the next while loop, this time we might not > >> do css_tryget(&last_visited->css) if the dead_count is changed, but > >> we still do css_put(&last_visited->css), we put it twice, this could > >> trigger the BUG_ON at kernel/cgroup.c:893. > > > > Yes, I guess your are right and I suspect that this has been silently > > fixed by 519ebea3bf6d ("mm: memcontrol: factor out reclaim iterator > > loading and updating"). I think a more appropriate fix is would be. > > Are you able to reproduce and re-test it? > > --- > > Yes, I think this commit can fix this issue, and I backport this > commit to 3.10.107 kernel and cannot reproduce this issue. I guess > this commit might need to be backported to 3.10.y stable kernel. Please send it to the kernel-stable mailing list. 3.10 seems to be still maintained. -- Michal Hocko SUSE Labs