On Wed 26-07-17 21:07:42, Wenwei Tao wrote:
> 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.
Yes, I guess your are right and I suspect that this has been silently
fixed by 519ebea3bf6d ("mm: memcontrol: factor out reclaim iterator
loading and updating"). I think a more appropriate fix is would be.
Are you able to reproduce and re-test it?
---
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 437ae2cbe102..0848ec05c12a 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1224,6 +1224,8 @@ struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
if (last_visited && last_visited != root &&
!css_tryget(&last_visited->css))
last_visited = NULL;
+ } else {
+ last_visited = true;
}
}
--
Michal Hocko
SUSE Labs
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