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Date: Sat, 9 May 2020 10:31:00 +0800
From: Yang Yingliang <yangyingliang@...wei.com>
To: Zefan Li <lizefan@...wei.com>, Tejun Heo <tj@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <cgroups@...r.kernel.org>,
<netdev@...r.kernel.org>,
"Libin (Huawei)" <huawei.libin@...wei.com>, <guofan5@...wei.com>,
<wangkefeng.wang@...wei.com>
Subject: Re: cgroup pointed by sock is leaked on mode switch
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@...wei.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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