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@xxxxxxxxxx
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
.
