[RFC PATCH] mm: memcg: fix css double put in mem_cgroup_iter
From: Wenwei Tao
Date: Wed Jul 26 2017 - 09:08:22 EST
From: Wenwei Tao <wenwei.tww@xxxxxxxxxxxxxxx>
By removing the child cgroup while the parent cgroup is
under reclaim, we could trigger the following kernel panic
on kernel 3.10:
------------------------------------------------------------------------
kernel BUG at kernel/cgroup.c:893!
invalid opcode: 0000 [#1] SMP
CPU: 1 PID: 22477 Comm: kworker/1:1 Not tainted 3.10.107 #1
Workqueue: cgroup_destroy css_dput_fn
task: ffff8817959a5780 ti: ffff8817e8886000 task.ti: ffff8817e8886000
RIP: 0010:[<ffffffff810cd6e0>] [<ffffffff810cd6e0>]
cgroup_diput+0xc0/0xf0
RSP: 0000:ffff8817e8887da0 EFLAGS: 00010246
RAX: 0000000000000000 RBX: ffff8817a5dd5d40 RCX: dead000000000200
RDX: 0000000000000000 RSI: ffff8817973a6910 RDI: ffff8817f54c2a00
RBP: ffff8817e8887dc8 R08: ffff8817a5dd5dd0 R09: df9fb35794b01820
R10: df9fb35794b01820 R11: 00007fa95b1efcda R12: ffff8817a5dd5d9c
R13: ffff8817f38b3a40 R14: ffff8817973a6910 R15: ffff8817973a6910
FS: 0000000000000000(0000) GS:ffff88181f220000(0000)
knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa6e6234000 CR3: 000000179f19d000 CR4: 00000000000407e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Stack:
ffff8817a5dd5d40 ffff8817a5dd5d9c ffff8817f38b3a40 ffff8817973a6910
0000000000000040 ffff8817e8887df8 ffffffff811b37c2 ffff8817fa23c000
ffff8817f57dbb80 ffff88181f232ac0 ffff88181f237500 ffff8817e8887e10
Call Trace:
[<ffffffff811b37c2>] dput+0x1a2/0x2f0
[<ffffffff810cbacc>] cgroup_dput.isra.21+0x1c/0x30
[<ffffffff810cbafd>] css_dput_fn+0x1d/0x20
[<ffffffff81078ebc>] process_one_work+0x17c/0x460
[<ffffffff81079b66>] worker_thread+0x116/0x3b0
[<ffffffff81079a50>] ? manage_workers.isra.25+0x290/0x290
[<ffffffff81080330>] kthread+0xc0/0xd0
[<ffffffff81080270>] ? insert_kthread_work+0x40/0x40
[<ffffffff815b1e08>] ret_from_fork+0x58/0x90
[<ffffffff81080270>] ? insert_kthread_work+0x40/0x40
Code: 41 5e 41 5f 5d c3 0f 1f 44 00 00 48 8b 7f 78 48 8b 07 a8 01 74 15
48 81 c7 30 01 00 00 48 c7 c6 a0 a7 0c 81 e8 b2 83 02 00 eb c8 <0f> 0b
49 8b 4e 18 48 c7 c2 7e f1 7a 81 be 85 03 00 00 48 c7 c7
RIP [<ffffffff810cd6e0>] cgroup_diput+0xc0/0xf0
RSP <ffff8817e8887da0>
---[ end trace 85eeea5212c44f51 ]---
------------------------------------------------------------------------
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.
Reported-by: Wang Yu <yuwang.yuwang@xxxxxxxxxxxxxxx>
Tested-by: Wang Yu <yuwang.yuwang@xxxxxxxxxxxxxxx>
Signed-off-by: Wenwei Tao <wenwei.tww@xxxxxxxxxxxxxxx>
---
mm/memcontrol.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 437ae2c..3d7a046 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1230,8 +1230,10 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
memcg = __mem_cgroup_iter_next(root, last_visited);
if (reclaim) {
- if (last_visited && last_visited != root)
+ if (last_visited && last_visited != root) {
css_put(&last_visited->css);
+ last_visited = NULL;
+ }
iter->last_visited = memcg;
smp_wmb();
--
1.8.3.1