Messages in this thread | | | Subject | Re: cgroup pointed by sock is leaked on mode switch | From | Yang Yingliang <> | Date | Sat, 9 May 2020 10:31:00 +0800 |
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On 2020/5/6 15:51, Zefan Li wrote: > On 2020/5/6 10:16, Zefan Li wrote: >> 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 */ >> > > Correction (still not tested): > > # mount -t cgroup2 none /cgroup/v2 > # mkdir /cgroup/v2/xxx > # echo PID > /cgroup/v2/xxx/cgroup.procs > /* this PID process starts to do some network thing */ > > # mount -t cgroup -o netprio xxx /cgroup/netprio > # mkdir /cgroup/netprio/xxx > # echo PID > /cgroup/netprio/xxx/tasks > ... > /* the PID process exits */ > > rmdir /cgroup/netprio/xxx > rmdir /cgroup/v2/xxx > /* now looks like this v2 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; > I've do some test with this change, here is the test result:
Without this change, nr_dying_descendants is increased and the cgroup is leaked:
linux-dVpNUK:~ # mount | grep cgroup tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755) cgroup2 on /sys/fs/cgroup/unified type cgroup2 (rw,nosuid,nodev,noexec,relatime,nsdelegate) cgroup on /sys/fs/cgroup/systemd type cgroup (rw,nosuid,nodev,noexec,relatime,xattr,name=systemd) cgroup on /sys/fs/cgroup/blkio type cgroup (rw,nosuid,nodev,noexec,relatime,blkio) cgroup on /sys/fs/cgroup/cpu,cpuacct type cgroup (rw,nosuid,nodev,noexec,relatime,cpu,cpuacct) cgroup on /sys/fs/cgroup/net_cls,net_prio type cgroup (rw,nosuid,nodev,noexec,relatime,net_cls,net_prio) cgroup on /sys/fs/cgroup/freezer type cgroup (rw,nosuid,nodev,noexec,relatime,freezer) cgroup on /sys/fs/cgroup/devices type cgroup (rw,nosuid,nodev,noexec,relatime,devices) cgroup on /sys/fs/cgroup/memory type cgroup (rw,nosuid,nodev,noexec,relatime,memory) cgroup on /sys/fs/cgroup/cpuset type cgroup (rw,nosuid,nodev,noexec,relatime,cpuset) cgroup on /sys/fs/cgroup/perf_event type cgroup (rw,nosuid,nodev,noexec,relatime,perf_event) cgroup on /sys/fs/cgroup/pids type cgroup (rw,nosuid,nodev,noexec,relatime,pids) cgroup on /sys/fs/cgroup/hugetlb type cgroup (rw,nosuid,nodev,noexec,relatime,hugetlb) linux-dVpNUK:~ # mkdir /sys/fs/cgroup/net_cls,net_prio/test linux-dVpNUK:~ # ps -ef | grep bash root 12151 12150 0 00:31 pts/0 00:00:00 -bash root 12322 12321 0 00:31 pts/1 00:00:00 -bash root 12704 12703 0 00:31 pts/2 00:00:00 -bash root 13359 12704 0 00:31 pts/2 00:00:00 grep --color=auto bash linux-dVpNUK:~ # echo 12151 > /sys/fs/cgroup/net_cls,net_prio/test/tasks linux-dVpNUK:~ # echo 12322 > /sys/fs/cgroup/net_cls,net_prio/test/tasks
(Use bash(12151/12322) do some network things, then kill them, the nr_dying_descendants is increased.) linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 1 /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 linux-dVpNUK:~ # kill 12151 12322 linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 3 /sys/fs/cgroup/unified/user.slice/cgroup.stat:nr_dying_descendants 2 /sys/fs/cgroup/unified/user.slice/user-0.slice/cgroup.stat:nr_dying_descendants 2 /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
(after rmdir test, the nr_dying_descendants is not decreased.) linux-dVpNUK:~ # rmdir /sys/fs/cgroup/net_cls,net_prio/test linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 3 /sys/fs/cgroup/unified/user.slice/cgroup.stat:nr_dying_descendants 2 /sys/fs/cgroup/unified/user.slice/user-0.slice/cgroup.stat:nr_dying_descendants 2 /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
With this change, nr_dying_descendants is not increased:
linux-dVpNUK:~ # mkdir /sys/fs/cgroup/net_cls,net_prio/test linux-dVpNUK:~ # ps -ef | grep bash root 5466 5443 0 00:50 pts/1 00:00:00 -bash root 5724 5723 0 00:50 pts/2 00:00:00 -bash root 6701 17013 0 00:50 pts/0 00:00:00 grep --color=auto bash root 17013 17012 0 00:46 pts/0 00:00:00 -bash linux-dVpNUK:~ # echo 5466 > /sys/fs/cgroup/net_cls,net_prio/test/tasks linux-dVpNUK:~ # echo 5724 > /sys/fs/cgroup/net_cls,net_prio/test/tasks linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 1 /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 linux-dVpNUK:~ # kill 5466 5724 linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 1 /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 linux-dVpNUK:~ # rmdir /sys/fs/cgroup/net_cls,net_prio/test/ linux-dVpNUK:~ # find /sys/fs/cgroup/ -name cgroup.stat -exec grep '^nr_dying_descendants [^0]' {} + /sys/fs/cgroup/unified/cgroup.stat:nr_dying_descendants 1 /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
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