Messages in this thread Patch in this message | | | Subject | Re: cgroup pointed by sock is leaked on mode switch | From | Zefan Li <> | Date | Wed, 6 May 2020 10:16:27 +0800 |
| |
On 2020/5/6 9:50, Yang Yingliang wrotee: > +cc lizefan@huawei.com > > On 2020/5/6 0:06, Tejun Heo wrote: >> Hello, Yang. >> >> On Sat, May 02, 2020 at 06:27:21PM +0800, Yang Yingliang wrote: >>> I find the number nr_dying_descendants is increasing: >>> linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep >>> '^nr_dying_descendants [^0]' {} + >>> /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 80 >>> /sys/fs/cgroup/unified/system.slice/cgroup.stat:nr_dying_descendants 1 >>> /sys/fs/cgroup/unified/system.slice/system-hostos.slice/cgroup.stat:nr_dying_descendants >>> 1 >>> /sys/fs/cgroup/unified/lxc/cgroup.stat:nr_dying_descendants 79 >>> /sys/fs/cgroup/unified/lxc/5f1fdb8c54fa40c3e599613dab6e4815058b76ebada8a27bc1fe80c0d4801764/cgroup.stat:nr_dying_descendants >>> 78 >>> /sys/fs/cgroup/unified/lxc/5f1fdb8c54fa40c3e599613dab6e4815058b76ebada8a27bc1fe80c0d4801764/system.slice/cgroup.stat:nr_dying_descendants >>> 78 >> Those numbers are nowhere close to causing oom issues. There are some >> aspects of page and other cache draining which is being improved but unless >> you're seeing numbers multiple orders of magnitude higher, this isn't the >> source of your problem. >> >>> The situation is as same as the commit bd1060a1d671 ("sock, cgroup: add >>> sock->sk_cgroup") describes. >>> "On mode switch, cgroup references which are already being pointed to by >>> socks may be leaked." >> I'm doubtful that you're hitting that issue. Mode switching means memcg >> being switched between cgroup1 and cgroup2 hierarchies, which is unlikely to >> be what's happening when you're launching docker containers. >> >> The first step would be identifying where memory is going and finding out >> whether memcg is actually being switched between cgroup1 and 2 - look at the >> hierarchy number in /proc/cgroups, if that's switching between 0 and >> someting not zero, it is switching. >>
I think there's a bug here which can lead to unlimited memory leak. This should reproduce the bug:
# mount -t cgroup -o netprio xxx /cgroup/netprio # mkdir /cgroup/netprio/xxx # echo PID > /cgroup/netprio/xxx/tasks /* this PID process starts to do some network thing and then exits */ # rmdir /cgroup/netprio/xxx /* now this cgroup will never be freed */
Look at the code:
static inline void sock_update_netprioidx(struct sock_cgroup_data *skcd) { ... sock_cgroup_set_prioidx(skcd, task_netprioidx(current)); }
static inline void sock_cgroup_set_prioidx(struct sock_cgroup_data *skcd, u16 prioidx) { ... if (sock_cgroup_prioidx(&skcd_buf) == prioidx) return ; ... skcd_buf.prioidx = prioidx; WRITE_ONCE(skcd->val, skcd_buf.val); }
task_netprioidx() will be the cgrp id of xxx which is not 1, but sock_cgroup_prioidx(&skcd_buf) is 1 because it thought it's in v2 mode. Now we have a memory leak.
I think the eastest fix is to do the mode switch here:
diff --git a/net/core/netprio_cgroup.c b/net/core/netprio_cgroup.c index b905747..2397866 100644 --- a/net/core/netprio_cgroup.c +++ b/net/core/netprio_cgroup.c @@ -240,6 +240,8 @@ static void net_prio_attach(struct cgroup_taskset *tset) struct task_struct *p; struct cgroup_subsys_state *css;
+ cgroup_sk_alloc_disable(); + cgroup_taskset_for_each(p, css, tset) { void *v = (void *)(unsigned long)css->cgroup->id;
| |