Issue

• A process was blocked in D state at mutex_lock() after kmem_cache_destory_memcg_children(), and the system crashed with Kernel panic - not syncing: hung_task: blocked tasks message.

crash> bt 6982
PID: 6982   TASK: ffff8800d2f64e70  CPU: 7   COMMAND: "dockerd"
 #0 [ffff8800a9fcfb40] __schedule at ffffffff8168af25
 #1 [ffff8800a9fcfba8] schedule_preempt_disabled at ffffffff8168c669
 #2 [ffff8800a9fcfbb8] __mutex_lock_slowpath at ffffffff8168a2c5
 #3 [ffff8800a9fcfc10] mutex_lock at ffffffff8168972f
 #4 [ffff8800a9fcfc28] kmem_cache_destroy_memcg_children at ffffffff811f3cfe
 #5 [ffff8800a9fcfc50] kmem_cache_destroy at ffffffff811a56d9
 #6 [ffff8800a9fcfc70] bioset_free at ffffffff8123741e
 #7 [ffff8800a9fcfc90] __dm_destroy at ffffffffa00029de [dm_mod]
 #8 [ffff8800a9fcfcd0] dm_destroy at ffffffffa0003833 [dm_mod]
 #9 [ffff8800a9fcfce0] dev_remove at ffffffffa00093de [dm_mod]
#10 [ffff8800a9fcfd10] ctl_ioctl at ffffffffa0009a35 [dm_mod]
#11 [ffff8800a9fcfea8] dm_ctl_ioctl at ffffffffa0009d63 [dm_mod]
#12 [ffff8800a9fcfeb8] do_vfs_ioctl at ffffffff81211ed5
#13 [ffff8800a9fcff30] sys_ioctl at ffffffff81212151
#14 [ffff8800a9fcff80] system_call_fastpath at ffffffff816964c9
    RIP: 00007f5a74036567  RSP: 00007f5a1cfd0b40  RFLAGS: 00000293
    RAX: 0000000000000010  RBX: ffffffff816964c9  RCX: ffffffffffffffff
    RDX: 00007f5a0c01d4a0  RSI: 00000000c138fd04  RDI: 000000000000000a
    RBP: 00007f5a74354ef3   R8: 0000000000000001   R9: 0000000000010b60
    R10: 00007f5a0c000078  R11: 0000000000000246  R12: 00007f5a1cfd0bd0
    R13: 00007f5a0c01d3c0  R14: 00007f5a74354ef3  R15: 00007f5a7435503a
    ORIG_RAX: 0000000000000010  CS: 0033  SS: 002b

• A process was blocked in D state at mutex_lock() after kmem_cache_destroy_memcg_children(). The kmem_cache_destroy_memcg_childre() was called once again from kmem_cache_destroy().

crash> bt 0xffff88078aed2f10
PID: 45393  TASK: ffff88078aed2f10  CPU: 1   COMMAND: "kworker/u128:4"
 #0 [ffff8800cfb8bba0] __schedule at ffffffff8168af25
 #1 [ffff8800cfb8bc08] schedule_preempt_disabled at ffffffff8168c669
 #2 [ffff8800cfb8bc18] __mutex_lock_slowpath at ffffffff8168a2c5
 #3 [ffff8800cfb8bc70] mutex_lock at ffffffff8168972f
 #4 [ffff8800cfb8bc88] kmem_cache_destroy_memcg_children at ffffffff811f3cfe
 #5 [ffff8800cfb8bcb0] kmem_cache_destroy at ffffffff811a56d9
 #6 [ffff8800cfb8bcd0] kmem_cache_destroy_memcg_children at ffffffff811f3d49
 #7 [ffff8800cfb8bcf8] kmem_cache_destroy at ffffffff811a56d9
 #8 [ffff8800cfb8bd18] nf_conntrack_cleanup_net_list at ffffffffa034a5db [nf_conntrack]
 #9 [ffff8800cfb8bd60] nf_conntrack_pernet_exit at ffffffffa034b45d [nf_conntrack]
#10 [ffff8800cfb8bd88] ops_exit_list at ffffffff815667f3
#11 [ffff8800cfb8bdb8] cleanup_net at ffffffff815678d0
#12 [ffff8800cfb8be20] process_one_work at ffffffff810a7f3b
#13 [ffff8800cfb8be68] worker_thread at ffffffff810a8d76
#14 [ffff8800cfb8bec8] kthread at ffffffff810b052f
#15 [ffff8800cfb8bf50] ret_from_fork at ffffffff81696418