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I'm currently using my phone as a wireless AP to acquire the Internet on my laptop which is currently on Debian Stretch. I can use multiple SIM card on my phone, and I happen to switch between them frequently while keeping my laptop connected by WiFi. When I do this, Network Manager behaves strangely and won't respond to systemctl stop network-manager. If I try to reboot my laptop, the shutdown procedure seems to be stopped by systemctl trying to end network-manager.service.

I have given this some thought, and I think that it might be related to DHCP, but I don't know how to get around this issue.

Edit: Here's dmesg output when this happens:

[18960.430501] ath10k_pci 0000:01:00.0: timed out waiting for offchannel skb ffff9f61de9f6100
[18963.502564] ath10k_pci 0000:01:00.0: timed out waiting for offchannel skb ffff9f61de9f6100
[18966.574459] ath10k_pci 0000:01:00.0: timed out waiting for offchannel skb ffff9f61de9f6100
[18969.646485] ath10k_pci 0000:01:00.0: timed out waiting for offchannel skb ffff9f61de9f6100
[18972.206627] INFO: task NetworkManager:479 blocked for more than 120 seconds.
[18972.206634]       Not tainted 4.9.0-8-amd64 #1 Debian 4.9.130-2
[18972.206636] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[18972.206639] NetworkManager  D    0   479      1 0x00000000
[18972.206643]  ffff9f620673e040 0000000000000000 ffff9f62063f9100 ffff9f6211c98980
[18972.206647]  ffff9f620c58a080 ffffbac100f3fb78 ffffffff96e14219 0000000000000000
[18972.206650]  00ff9f62083cbc01 ffff9f6211c98980 000011078562377a ffff9f62063f9100
[18972.206653] Call Trace:
[18972.206663]  [<ffffffff96e14219>] ? __schedule+0x239/0x6f0
[18972.206666]  [<ffffffff96e14702>] ? schedule+0x32/0x80
[18972.206669]  [<ffffffff96e149aa>] ? schedule_preempt_disabled+0xa/0x10
[18972.206672]  [<ffffffff96e16404>] ? __mutex_lock_slowpath+0xb4/0x130
[18972.206675]  [<ffffffff96d48860>] ? genl_family_rcv_msg+0x360/0x360
[18972.206677]  [<ffffffff96e1649b>] ? mutex_lock+0x1b/0x30
[18972.206681]  [<ffffffff96d48911>] ? genl_rcv_msg+0xb1/0xc0
[18972.206683]  [<ffffffff96d47e64>] ? netlink_rcv_skb+0xa4/0xc0
[18972.206685]  [<ffffffff96d484e4>] ? genl_rcv+0x24/0x40
[18972.206687]  [<ffffffff96d4783a>] ? netlink_unicast+0x18a/0x230
[18972.206688]  [<ffffffff96d47c37>] ? netlink_sendmsg+0x357/0x3b0
[18972.206692]  [<ffffffff96cf2946>] ? sock_sendmsg+0x36/0x40
[18972.206694]  [<ffffffff96cf33d8>] ? ___sys_sendmsg+0x2c8/0x2e0
[18972.206697]  [<ffffffff96a20630>] ? poll_select_copy_remaining+0x150/0x150
[18972.206699]  [<ffffffff96a20630>] ? poll_select_copy_remaining+0x150/0x150
[18972.206701]  [<ffffffff96a20630>] ? poll_select_copy_remaining+0x150/0x150
[18972.206703]  [<ffffffff96a20630>] ? poll_select_copy_remaining+0x150/0x150
[18972.206705]  [<ffffffff96a53f1f>] ? ep_poll+0x32f/0x350
[18972.206707]  [<ffffffff96cf3ce1>] ? __sys_sendmsg+0x51/0x90
[18972.206710]  [<ffffffff96803b7d>] ? do_syscall_64+0x8d/0xf0
[18972.206713]  [<ffffffff96e18f8e>] ? entry_SYSCALL_64_after_swapgs+0x58/0xc6

This output loops through the dmesg logs as soon as Network Manager starts acting strangely. Also, to get this output, I had to run dmesg with the follow option before this happens; because neither dmesg nor systemctl respond after the offchannel error loops in dmesg logs.

Edit:What was said above triggers indeed this issue, but it can also happen for no apparent reason.

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